Why do people comment when it's a spot-on answer? I often get useful comments like the first comment here, but wonder why they don't post those as answers. If they post them as answers, I can boost their reps by upvoting and choose "solved" but I can't do that with comments. Is it for readability or something? I don't have to scroll much to see comments, and that's convenient, but are there other reasons why people do this?
I think it indicates a degree of uncertainty about whether the content if their comment is of high enough quality to constitute an answer.
Since comments are intended to be mainly for seeking clarifications to posts, I think answers in comments would sometimes be better posted as answers.
However, for more skeletal answers in comments it may be preferable to flesh them out before posting as answers.