The point so you can achieve the perfect gas/brake ratio needed for a good drift. Toe on gas same time heel is on brake thrugh the turn

Heel-toe is generally used for shifting down gears, and it is all about balance. When you shift down gear you are increasing the engine braking/acceleration force through the wheels. If I am driving a rear-wheel-drive car in fourth gear at 3,000rpm and I suddenly clutch and shift down to third and release the clutch from idling revs, the drivetrain takes up the shock of the engine being forced to speed up to match the wheels. There is a possibility that instead of the engine matching the wheel-speed, the wheels will suddenly slow down to match the engine speed - compression lockup. Compression lockup can have the same effect on a car as if you pulled the handbrake (e-brake) on while moving. This can unbalance the car and cause you to lose control. Heel-toe shifting can be used with or without double-clutching, but basically you use the heel of the foot to press the throttle while using the toes/ball of your foot to press the brake. As you shift down the gear, you 'blip' the throttle to rev the engine. If done correctly this should match the engine speed to the wheels' speed, and when you release the clutch there is no shock on the drivetrain - the car stays balanced, and if you're downshifting for a corner, then you haven't had to take your foot off the brake to do the smooth gear change. When drifting, balance is of the utmost importance, hence heel-toe shifting is very useful.