The main reason we dumped (both times) was simply to get the aircraft down to landing weight. We were approximately 25 tons above Max Landing Weight at the time and so dumped that amount of fuel. Rather an expensive exercise really! Obviously you still have the option to land overweight if you don't have the time to dump, however if you do have the time, and subsequently land overweight and do some damage, I imagine that the subsequent board of inquiry's first question would be "Why didn't you dump?"
Obviously, nothing takes away the commander's authority to land immediately (overweight if necessary) if he/she feels the flight to be in immediate danger.
I can't think of a fault which might actually require you to dump fuel as part of the drill. Of course that doesn't mean there isn't one!!
Cheers all
