What's the advantage of closing a thread over permasageing it?

Like a closed thread, permasaged threads don't clutter the recent topics list, but it's still possible for especially interested people to carry on the conversation without disturbing others. Maybe there'll be some last-minute insight that's worthy of basing a new thread on. Permasage is like a warning that tells posters in badly degenerated threads to get their act together. Or maybe it'll allow everyone involved to conclude with some last words and move on; much less oppressive than suddenly declaring that the discussion is over.