Good discussion!!! When entering a corner, let's say in third gear at 95 mph, you'll want to brake for the turn and get into the next lowest gear for better launch in the exit. In many corners this is best accomplished DURING the braking process by tipping your brake foot over and blipping the throttle to match revs for the downshift. In the 95 mph model, you would brake hard, blip the throttle and slip into second at around 70 mph and 6.5K rpm.
Imagine just dumping the car into second at 70 mph with the revs at, say, 3K rpm because you have failed to rev the engine (we've all done that once or twice). The car lurches down in speed and transfers all it's weight onto the front tires, unweighting the rears. Now imagine disrupting the balance of the car in that way in the middle of a 70 mph corner. Spin time!
If you have successfully matched the rpm of the engine to the transmission, then that disruptive weight transfer and subsequent loss of control won't happen, and you're in the correct gear to launch you out of the corner.
Practice downshifting without matching revs and then with it (without braking) and you'll see how much more the car stays in balance.
I have practiced this on empty roads at slow speeds for some time, and I'm still working on perfecting my technique, both on the street and the track.
Hope I was of some help. A good source is "Going Faster!" by Skip Barber (it's my personal track bible. I bring it to every event to remind me of the important stuff!)