[1] It is most commonly used in auto racing, where simultaneous gas and brake keeps revs up, and in turbocharged vehicles keeps pressure up and reduces turbo lag.
[3][4] It is closely related to the handbrake turn, but involves locking the rear wheels using the foot brake (retarding actually, to reduce traction, rarely fully locking – best considered a misapplication), which is set up to apply a significant pressure bias to the rear brakes.
[5] In restrictor plate NASCAR events, drivers were known to left-foot-brake at times, particularly in heavy traffic situations.
Rather than lift off the throttle, which could lose considerable power and speed (due to the restrictor plates), a mild tap of the brakes while the right foot was still planted flat on the gas, could help avoid contact and bump drafting.
Critics of the technique suggest that it can cause confusion when switching to or from a vehicle with a manual transmission,[7] and that it is difficult to achieve the necessary sensitivity to brake smoothly when one's left foot is accustomed to operating a clutch pedal.
[7][8] However, some commentators do recommend left-foot braking as routine practice when driving vehicles fitted with an automatic transmission, when maneuvering at low speeds.