The only use I see is to slow down adds while questing or on certain specific tasks during raids (Dunno whether they exist in ToT yet)
Given the removal of Freeze, I would love it if they made Blizzard a spell that didn't need to be channelled, so that we could generate FoF during add fights (similar to destro locks with Rain of Fire) and this could also be used situationally to get some on demand burst.
Thoughts? Is there any particular boss in this tier where Frost mages uses Blizzard at all?