I always think it odd when one asks an open ended question and puts their own answer in the top text. It biases the conversation. That shit goes in the first comment.
I do sometimes when I feel like its contextually appropriate. I edit comments too. I see it more as a comment being one unit of conversation, so if I made a mistake I'll edit it (usually leaving the edited content crossed out for context). If I have kind of a side story/topic, I'll sometimes reply to myself with it. If I have multiple distinct thoughts/ideas I'll make two comments.
There's some advantages, such as them being upvotable and commentable separately. Separate votes and discussion for option A and B.