Heel and toe is because the driver is taking the corner as fast as possible, on the verge of the car sliding off of the track. When they come off of the straight away they are braking heavily into the corner. When you downshift and release the clutch the engine revs must be high enough so that your engine doesn't slow down the rear wheels which would cause you to spin off the track. It is something which should never be necessary on the street unless you just robbed a bank.