The Archival is used as a testing ground by some members. I have seen campaign managers and ANN thread creators post threads there to check how they look before creating the official thread in another section of the forum. I don't know if the use cases for Archival changed throughout the years, but here is what theymos had to say about it in one of his posts:

It was never intended to be a graveyard, but theymos doesn't mind that it became one. Maybe someone else has some more information about the "rare situations" it was supposed to be used for.