"There's more to braking than just latching on to the brakes at the top of a hill. If you brake that way with either discs or rim, you really aren't getting the most out of your brakes and you could cause damage to either system...although the discs might take longer to show the problems. There's also the fact that to ride that way is incredibly slow." --cyccommute

Just was thinking about a worst case scenario of a loaded tourer with trailer decending, not attempting to promote improper braking.

Brad