I admit I'm not that well verse in Halo technology, but why do they use Cryo on ships that can go FTL?
They can go FTL, but it still takes weeks or months to get from one place to another. It's more economical to ice down part of or (if there's an AI to handle the revival) all of the crew than to bring along enough supplies for everybody to be awake during the journey.
You also don't have to worry about them going stir-crazy. Perhaps less of a problem on a capital ship like the Pillar of Autumn
, but in a two-person shuttle...?