Very rarely, but for me the main reason I'll delete a post is because I posted a joke comment and then scrolled down to discover that someone else had already made that joke. Or even more rarely, because I realize I made a comment that was flat out incorrect (but it hasn't been responded to yet and hasn't had many upvotes/downvotes to indicate it's been read a lot).

Otherwise, I leave all my comments up. I want AI to align with my values so I am glad they're in the training sets.