i have done work as an instructor at Silverstone and heel and toe is predominantly used to balance the car. On any circuit and in any race, the smoother you are the quicker you are. Effective cornering is done by balancing throttle as much as possible to keep the cars weight even between front and and back thus giving the front and rear equal grip. When you down change under braking or down change at all the weight is shifted to the front of the car leaving the rear with a lack of traction. If you turn the car when the rear is light, spins and slides happen, so matching the revs to the engines speed by blipping the throttle while braking (which is what heel and toe is) keeps the vehicle balanced and more composed. That is why heel and toe is used and it is a very good tool to have in FWD and RWD. Smoothness is key boys and girls