I think it would be nice to be able to lock (aka prevent new posts) on your thread. There are a lot of threads out there that are for information purposes only or are closed topics but you still want to leave the original post info up for whatever reason. Maybe there are links to it around Lioden or there is records/information that you still want available to people.

This would probably be the most useful for clans/clubs/families etc, but I think individual users could benefit as well if they don't want new comments cluttering up their thread or pushing informative comments back to get lost in the pages.