When I flag an answer as "not an answer" and it is accepted by a moderator, is the user who posted the answer notified about this? Does this notification contain an explanation why the answer was removed?
I am asking because I never know if I should post comments explaining that the answer was flagged and what it means.
The flag itself doesn't send out any notification.
If the answer is deleted or converted to a comment and the moderator who does that leaves a comment, the user will be notified of that comment.
I typically leave comments on most not-an-answers that I remove if they're recently posted. There's not much point in commenting on something that's over a year old, for example.
You can certainly leave a comment of your own, especially since there may be enough time for the user to see it before a moderator sees your flag. You can use a handy userscript to store and reuse the most common comments. It comes with a few pre-loaded that you can use right away, but I like to edit them to make the language more "mine".
Yes. The user will be able to see a link Why was this deleted? under the deleted answer if they go to the page directly. It also indicates if something was converted to a comment, instead of just deleted.
No direct poke is sent their way, however. But, if it's an answer they really cared about, they'll see why. Additionally, moderators can leave a comment prior to deleting that the user will see. We do this when helping new users, or chronic 'non-answerers'.
