I was talking about other turbo drivers telling me I needed to left foot brake to keep the throttle on and thusly turbo spooled. That is NOT a good reason to left foot brake.
The first advantage of left foot braking is no off throttle transition in the brake zone between throttle and brake. You go deeper into the corner because you don't have to lift then brake.
The second advantage to left foot braking is that you more control of the speed through the apex of the corner. With right foot braking if you brake too much, there is that transition time to get back on the throttle to make speed corrections. You are limited to bumping the throttle to control the corner speed. With left foot braking you are using both brakes and throttle to control the speed so if you over brake you have throttle there to compensate quicker. Or more accurately if you are going too fast you are braking to slow instead of coasting.
Here is a very good comparison between Schumacher (left foot braking) and Barrichello (right foot braking).
I've tried to learn left foot braking and frankly I can do well into and through the corner. My problem comes after the corner as I am upshifting. I forget to move my left foot off the brake and bang my head against the windshield pushing in what I think is the clutch.
The big thing to remember both when learning left foot braking and right foot heal/toe is to plant your heel on the floor. This forces you to use your calf muscles to control the pedal pressure instead of your thigh muscles. While your thigh is great for the on-off pumping of the clutch, it is not very good at the control required for threshold braking.
There are some great rally car videos out there that show the driver's feet dancing between left foot and heel/toe braking.