I have upgraded rear brakes (duh) and use pad choice in teh rear to help how the car behaves under braking and entering a corner coming off the brakes - A stronger pad, and the car wil lbrake more evenly, not nosedive, and stay very planted and stable, a weaker rera pad and the car nosedives more, transfers more weight towards the front, and sometimes get squirrely (an extreme case is the saturn, with it's rear drums... no rear braking, nosedives a lot, rear end starts to want to come around, then locks due to the lack of weight on the tires - let me tell ya, THAT's exciting
) this helps turn-in a little by getting more weight on the front tires, and lets the rear end "come around" a little more as you begin to turn.
In essence, you can control the brake bias with rear pad selection without so much risk of completely destroying the car's braking behavior with a bias controler. with your "big" front brakes and stock rear, especially if you start adding real strong front pads, the car can get real squirrely under braking due to the weight transfer. I guess what i'm trying to say is that the rear brakes CAN do a lot more work than you're giving them credit for.