Why are posts withdrawn instead of being deleted immediately?

A member mass deleting their posts is a different issue. In terms of

(post withdrawn by author, will be automatically deleted in 24 hours unless flagged)

I know of no times any such post has been flagged. And as long as Moderators could see post history a topic could be flagged with a type of “hey, so+so called me a so+so then deleted it!” or whatever.

These timed deletes have gotten flagged for some forums?