Ok, thats called specifically trail braking in english not left foot braking, trail braking is carrying the brake into the apex in order to help the rear come around in tighter corners in cars that tend to be nose heavy and want to plow straight in the corner otherwise. Not ideal for a rear weight bias car and rear pivot point car such as the rear engined 911, since the rear tends to come around much easier without the need for trailbraking. Just like lift-off overteer technique.

I use this in the sportquad in difficult-to-slide corners when I want to powerslide out of the corner by helping the rear to brake loose easier beforehand by carrying the rear brake into the apex.

Left foot braking I believe refers more to keeping on the throttle for a little longer while you start to apply the brakes before a corner, therefore ovelapping the application of the throttle and brakes causing a smoother transition. F1 cars do this for example since the don't have a clutch pedal and left foot is always on the brake, and with 900HP, 600kg and the drag of a bus, the transitions of when you get off the throttle and start to brake can be a bit unsettleing. Schumacher uses this technique while his teamate Baricelo doesn't. F1 drivers that come from karting in their younger years tend to use this technique more often.

I use it when I go karting for a diffrent reason, I use it in order to keep the revs up to the maximun around the corner so as to have full power when exiting. The reason is because they are "automatic" karts, so when you lift the throttle for the corner the revs die down and when you get back on the throttle there is less power available until revs start to climb with speed. If you keep maintaining the throttle throughout the corner while using the brake (left foot) to cancel the tranfer of the torque to the rear wheels, you can maintain the throttle and the revs high, and went you exit and take off you let go of the brake.