Originally Posted by
Tomaski
Because at high altitude when you hit a wind shear or mountain wave and the speed starts moving rapidly toward Mmo, you need to use the speed brakes to slow instead of ripping the throttles toward idle. I've seen it done the other way, and it isn't pretty.
There could always be an auto-stowed at certain TLA or N1. If the jet was overspeeding, the TLA would be likely below or moving to a lower power setting with the A/T on.