Little video we threw together during testing at Knockhill racing circuit.
Heal toe is used during heavy braking where a downshift is requires to match the engine revs to the new gear. This helps maintain the car’s balance under braking and prevent locking the front wheels with the extra load engine braking would generate. As an additional bonus, it improves mechanical sympathy helping prevent damage to the gearboxes synchromesh.
Left foot braking is often used in rallying to adjust the yaw angle of the car mid corner which can stop it running wide. In circuit racing braking with your left foot where a downshift is not required allows you to trail brake and/or brake later in to the corner. It also removes the time required to switch from brake to throttle pedal allowing the driver to get back on the power sooner.