For motorcycles specifically, you want to be able to accelerate instantaneously to get out of trouble. You also want some throttle when coming out of a turn, and you don't want to declutch in the middle of a turn while leaned over. The acceleration is what stands the bike up, especially if you need to get out of an emergency situation. The throttle is your friend, but to use it, you can't have the engine disconnected from the wheels.
That makes sense for bikes, and of course I did do it in the truck then....otherwise, I'd have just coasted to a stop after the turn and would have looked quite the fool.
The rest of it....well, that makes sense. But man, at least here at the beginning, if I'm worrying about downshifting, I forget to brake. I can't tell you how many traffic cones I ran over that 1st day while thinking to myself "don't forget to shift down into 1st gear..." and totally forgetting to brake.