For some posts, the answer might be very short or a single line answer. so sometimes users post them in comments instead of as answer.
For example, Have a look at this Question. Bala left a comment on the post which is the answer for that.
So if I strongly believe that comment is an answer for that, can I elaborate and post that as an answer. So that it would be helpful for future readers.
If I do so, it would looks like I copied answer from comment.