That lists
"journal default" (allows whatever you set things for in the options area which are pretty much what these sections list),
"disable" (no comments at all),
"locked" (no more comments allowed - which I'm using now if it's an old post and it gets hit),
and "don't notify" (don't tell me if there are comments).

It only affects what appears to people who read it. The posts are still there and still gum up my backups to LJarchive.