I don't see an API call to delete messages. (Already posted to feedback, figured it would be worth posting here).
Possible reasonable use-cases:
1) Moderated channels
2) channel security scanner (maybe that looks for and deletes things like accidentally posted passwords or credit card info).
3) Obscenity filter (heh, replace the naughty with an appropriate subset of emoticons)
I'm sure if I thought about it I could think of others. I know, I can do it as admin - manually. Yucko.
-- Tom Bortels, causing trouble