Hyoroemon said:
Do flame post from 'banned' just stay here? I saw a troll account user #374156
who changed their name. I'm glad if they are banned but if left ugly sight such as in post #1245596
Yes. In general, only spam and flame wars are deleted. Discussions, however stupid they may be, usually stay, but the comments of users who multiple users disagree with are often voted down and thereby hidden by default.
Deleting one user’s comments from a discussion looks suspicious too and isn’t any better than hiding them anyway. Deleting the whole discussion seems unfair because the other users probably didn’t do anything wrong. Except for the aforementioned flame wars were everyone’s comments deserve to be deleted.
Btw, you should write user #374156 and post #1245596 and Danbooru will turn those into correct links for you.