Originally Posted by jalusbrian
Bring a moderator does not entail you to arbitrarily move people's posts
It depends on what forum you're in. Some places have moderators who frequently delete large quantities of material simply because the posts/topics disagree with their sock puppets and/or clique members (that's the only way they can "win" a debate).
At the other extreme are places where mods have no power of deletion (only administrators), so only illegal material is deleted -- leaving a clear record to justify things like banning.
This forum is a typical net message board in which topics and posts are routinely deleted, locked, and moved (moving generally occurs when topics are merged). All submissions should be considered ephemeral, although one notable difference between this place and the norm is the lack of concern over so-called "necro" -- posting in old topics. Some places are so concerned with this that they consider topics older than a few days "necro" when posted to.
4Chan even automatically deletes topics once they move off the main page which can happen in as little as fifteen minutes.