Mainly ornamental
As far as I can see, the purpose of the whole FISA organization is to conceal from the public gaze what amounts to blanket authorization for spying on anyone at all, for any or no reason.
Congress could just have made that legal. But it looks (a little) better to create a "court" and have it hand out authorizations in secret. Then any criticism can be met by claiming it's a proper judicial proceeding.
Biting the hand that feeds IT
