Well, it depends.

First, I'd like to clarify a point. "Normal moderators" (read that as non-super mods nor admins) do not have the ability the fully delete a post. The only option we have, as I remember from the time I spent moderating here, is what is called "soft-delete". This means that any moderator and above still sees the post, sees the reason why it has been deleted, it is simply invisible to normal users and guests.

Thus, the "proof" is never erased. I expect that super-mods and admins do exactly the same (there frankly is never any reason to fully delete a message fully). It would be good that people understood this, so I'll repeat it one more time:

Moderators do NOT delete anything. We simply hide it, when required.

As for the "it depends" statement I used to open this post, I would say that as with all the rules we are discussing, it will be up to the appreciation of the moderator, and will depend on the level of infraction. If someone is posting heinous comments, things which can actually hurt people, then the thread should be cleaned (this means, the post be soft-deleted, and the quotes be cleaned out as well.

If, however, someone is just being off-topic, as always, moving from a thread into a new thread is highly recommended over anything else.

BTW, Thanks Kathy for swinging by. Much appreciated to see your input.