Comments are ephemeral by nature, which means:

• The user who posted them or a moderator can delete them at any time, that's just stating a fact, I'm not discussing intent,
• Regular users have no way of seeing deleted comments, they are only available to moderators, in contrast with deleted questions and answers which can still be accessed by regular users with more than 10,000 reputation,
• Moderators don't have access to a central list of deleted comments, if they don't know that a comment was deleted they might never find out.

Strictly speaking, you should only post comments to:

• Request clarification from the author;
• Leave constructive criticism that guides the author in improving the post;
• Add relevant but minor or transient information to a post (e.g. a link to a related question, or an alert to the author that the question has been updated).

Any other comment is subject to deletion, and it's up to the moderator who responds to a comment flag or happens to see the comment by chance to decide whether to delete or not. You can safely assume that comments that follow the above guidelines will not be deleted, other than by mistake (we are only human, after all).

Now to put my other answer in perspective, it was answering a question regarding popular comments, and I think I provided enough evidence that popular comments usually don't follow the aforementioned guidelines, and thus are more noise than signal. You have nothing to fear when informative comments on your posts, however that doesn't mean that you shouldn't really try and work actually informative comments into your posts, other than being ephemeral comments are also less visible, and I think you'll agree with me that useful information deserves to be where it will be more easily discovered, and that's the question or the answer itself.

Some examples of actual comments that don't follow the guidelines and can be deleted at any time:

• +1 for the good looking screenshots : )
• +1... it's really very simple so there's no framework so far, just JSPs. But I could use a framework if it helps. Apparently several people are commenting on Wicket so I'll probably give that a look.
• (I hope this very real question for which, indisputably, there exist very valid answers, won't be closed)
• +1 but be careful, they're not all nice here, see what happened to this: programmers.stackexchange.com/users/39479
• thanks a lot for these infos, it's very interesting!

And if I go through my comments, I'm sure I'll find quite a few that should be deleted, certainly more than yours.

Lastly, one quite valid use for comments would be a courtesy ping. You went through all the trouble to call me out using a rather ironic tone, I would have appreciated a comment pointing me to this question, I just happened to find it by accident and that's not very nice. But I guess nice wasn't exactly what you were aiming for.

Comments are ephemeral by nature, which means:

• The user who posted them or a moderator can delete them at any time, that's just stating a fact, I'm not discussing intent,
• Regular users have no way of seeing deleted comments, they are only available to moderators, in contrast with deleted questions and answers which can still be accessed by regular users with more than 10,000 reputation,
• Moderators don't have access to a central list of deleted comments, if they don't know that a comment was deleted they might never find out.

Strictly speaking, you should only post comments to:

• Request clarification from the author;
• Leave constructive criticism that guides the author in improving the post;
• Add relevant but minor or transient information to a post (e.g. a link to a related question, or an alert to the author that the question has been updated).

Any other comment is subject to deletion, and it's up to the moderator who responds to a comment flag or happens to see the comment by chance to decide whether to delete or not. You can safely assume that comments that follow the above guidelines will not be deleted, other than by mistake (we are only human, after all).

Now to put my other answer in perspective, it was answering a question regarding popular comments, and I think I provided enough evidence that popular comments usually don't follow the aforementioned guidelines, and thus are more noise than signal. You have nothing to fear when informative comments on your posts, however that doesn't mean that you shouldn't really try and work actually informative comments into your posts, other than being ephemeral comments are also less visible, and I think you'll agree with me that useful information deserves to be where it will be more easily discovered, and that's the question or the answer itself.

Some examples of actual comments that don't follow the guidelines and can be deleted at any time:

• +1 for the good looking screenshots : )
• +1... it's really very simple so there's no framework so far, just JSPs. But I could use a framework if it helps. Apparently several people are commenting on Wicket so I'll probably give that a look.
• (I hope this very real question for which, indisputably, there exist very valid answers, won't be closed)
• +1 but be careful, they're not all nice here, see what happened to this: programmers.stackexchange.com/users/39479
• thanks a lot for these infos, it's very interesting!

And if I go through my comments, I'm sure I'll find quite a few that should be deleted, certainly more than yours.

Lastly, one quite valid use for comments would be a courtesy ping. You went through all the trouble to call me out using a rather ironic tone, I would have appreciated a comment pointing me to this question, I just happened to find it by accident and that's not very nice. But I guess nice wasn't exactly what you were aiming for.

Comments are ephemeral by nature, which means:

• The user who posted them or a moderator can delete them at any time, that's just stating a fact, I'm not discussing intent,
• Regular users have no way of seeing deleted comments, they are only available to moderators, in contrast with deleted questions and answers which can still be accessed by regular users with more than 10,000 reputation,
• Moderators don't have access to a central list of deleted comments, if they don't know that a comment was deleted they might never find out.

Strictly speaking, you should only post comments to:

• Request clarification from the author;
• Leave constructive criticism that guides the author in improving the post;
• Add relevant but minor or transient information to a post (e.g. a link to a related question, or an alert to the author that the question has been updated).

Any other comment is subject to deletion, and it's up to the moderator who responds to a comment flag or happens to see the comment by chance to decide whether to delete or not. You can safely assume that comments that follow the above guidelines will not be deleted, other than by mistake (we are only human, after all).

Now to put my other answer in perspective, it was answering a question regarding popular comments, and I think I provided enough evidence that popular comments usually don't follow the aforementioned guidelines, and thus are more noise than signal. You have nothing to fear when informative comments on your posts, however that doesn't mean that you shouldn't really try and work actually informative comments into your posts, other than being ephemeral comments are also less visible, and I think you'll agree with me that useful information deserves to be where it will be more easily discovered, and that's the question or the answer itself.

Some examples of actual comments that don't follow the guidelines and can be deleted at any time:

• +1 for the good looking screenshots : )
• +1... it's really very simple so there's no framework so far, just JSPs. But I could use a framework if it helps. Apparently several people are commenting on Wicket so I'll probably give that a look.
• (I hope this very real question for which, indisputably, there exist very valid answers, won't be closed)
• +1 but be careful, they're not all nice here, see what happened to this: programmers.stackexchange.com/users/39479
• thanks a lot for these infos, it's very interesting!

And if I go through my comments, I'm sure I'll find quite a few that should be deleted, certainly more than yours.

Lastly, one quite valid use for comments would be a courtesy ping. You went through all the trouble to call me out using a rather ironic tone, I would have appreciated a comment pointing me to this question, I just happened to find it by accident and that's not very nice. But I guess nice wasn't exactly what you were aiming for.

Comments are ephemeral by nature, which means:

• The user who posted them or a moderator can delete them at any time, that's just stating a fact, I'm not discussing intent,
• Regular users have no way of seeing deleted comments, they are only available to moderators, in contrast with deleted questions and answers which can still be accessed by regular users with more than 10,000 reputation,
• Moderators don't have access to a central list of deleted comments, if they don't know that a comment was deleted they might never find out.

Strictly speaking, you should only post comments to:

• Request clarification from the author;
• Leave constructive criticism that guides the author in improving the post;
• Add relevant but minor or transient information to a post (e.g. a link to a related question, or an alert to the author that the question has been updated).

Any other comment is subject to deletion, and it's up to the moderator who responds to a comment flag or happens to see the comment by chance to decide whether to delete or not. You can safely assume that comments that follow the above guidelines will not be deleted, other than by mistake (we are only human, after all).

Now to put my other answer in perspective, it was answering a question regarding popular comments, and I think I provided enough evidence that popular comments usually don't follow the aforementioned guidelines, and thus are more noise than signal. You have nothing to fear when informative comments on your posts, however that doesn't mean that you shouldn't really try and work actually informative comments into your posts, other than being ephemeral comments are also less visible, and I think you'll agree with me that useful information deserves to be where it will be more easily discovered, and that's the question or the answer itself.

Some examples of actual comments that don't follow the guidelines and can be deleted at any time:

• +1 for the good looking screenshots : )
• +1... it's really very simple so there's no framework so far, just JSPs. But I could use a framework if it helps. Apparently several people are commenting on Wicket so I'll probably give that a look.
• (I hope this very real question for which, indisputably, there exist very valid answers, won't be closed)
• +1 but be careful, they're not all nice here, see what happened to this: programmers.stackexchange.com/users/39479
• thanks a lot for these infos, it's very interesting!

And if I go through my comments, I'm sure I'll find quite a few that should be deleted, certainly more than yours.

Lastly, one quite valid use for comments would be a courtesy ping. You went through all the trouble to call me out using a rather ironic tone, I would have appreciated a comment pointing me to this question, I just happened to find it by accident and that's not very nice. But I guess nice wasn't exactly what you were aiming for.