If you see how the riders in motorsport sit up at the end of the straights to scrub speed off, or ridden flat out and tried it yourself on the track, you would certainly appreciate how much difference it makes Sitting upright on a 600 supersport, max indicated is about 140, tuck in, and the bike starts to accelerate to the top of its gearing (indicated 170)
I used the sitting up air brake style all the time on the track when braking off the long straights, it dropped the speed from 140 to 70 much quicker than if I just used the brakes.