Often, I will go to answer a question, and I will notice that someone commented on the question, which basically the answer. Why not just answer instead of commenting? If the answer to the question is in the comments but provided as an answer, should I still provide an answer just for the sake of clarity?
Sometimes users post answers as comment. Often this is because they think the comment should be expanded to qualify as an answer, but for them it is too much effort to write it. They are just helping the OP with a hint, not an entire answer.
Others don't think the question doesn't deserve a full answer and instead post a comment. I don't think this is particularly useful: either answer the question or don't comment at all. Those questions should be closed if they deserve to, or be answered if possible.
You are totally in your right to post an answer to a question that has received useful comments. You can expand on those to make your post a fully qualified answer, not just a small note.
Always answer in the answers, never in the comments
Comments are not for answering the question. They are, as laid out in the comment everywhere privilege, for when you want 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).
Further, the same document also outlines cases that comments should not be used for, including:
Answering a question or providing an alternate solution to an existing answer; instead, post an actual answer (or edit to expand an existing one);
So, no. Comments should explicitly not be used for answering.
Comments are not designed to hold answers and answering with them short-circuits site quality controls:
To quote from a meta on RPG.se:
Answering in comments does the following things.
- It bypasses question closes. They're closed for a reason.
- It provides an answer that can't be marked as an answer for future people's knowledge.
- It contributes to long comment debates as you can comment on an answer, but it's unclear what you're commenting on in a comment thread.
- It is "cheating" by locking your answer to the top. Answers with higher votes/accepted answers should go to the top to indicate their quality. Bypassing that by sticking your answer in a comment on the question is unacceptable.
- It bypasses all our quality control mechanisms: we can't downvote your "answer", edit it, or comment on it to request clarification or improvements. Answers also bump a question to the top so that people will scrutinize the answer; comments don't do this.
- It gets in the way of people who are busy using comments correctly to improve the question.
The long and short of it is, every part of how the site functions, all of which have lengthy justification as being part of the process of SE - rep, answers, accepts, edits, votes, etc. - is obviated by using comments for answers. So every good goal of all that functionality is nullified by this practice.
Not every site follows this, but I do strongly believe that it is bad practice for any site on the network to do it and that it actually negatively impacts the sites that allow it.1
The solution to comment-answers
The way we handle comment-answers on RPG.se is we encourage all community members to flag them as "No longer needed" or as "Something else" with message that says "comment answer". They are then promptly deleted by diamond moderators.
Note that this practice may vary site-to-site, but I think it is the most straightforward way to deal with them, and it has worked well for us.
Also, feel free to borrow information from the comments and use them in your answer if you want to, just give attribution where it is needed. Don't let the presence of a comment-answer dissuade you from giving a high-quality answer to a question (this is one of the ways comment-answers materially hurt sites that allow them).
1 - Admittedly, on big sites like SO, this would be extremely hard to implement now that the practice is fairly entrained.