if you had a power loss / or interruption (part of why there are 3 (do I have that right) in a given aircraft ???) ... then, not only do you need to reset location and direction, you have to establish wings level, nose pitch X, (zero, I assume) to re-establish correct attitude sensing from which the gyro can reference.
As well as 3 they should also have pri & sec power supplies, sec normally is an emergency battery. I also remember (training course a few years back) they have a degraded mode of operation, ATT mode, no position input needed and much quicker alignment, however i'm not an Airbus engineer so cannot confirm if they are the same.