"the" tutorial? i wasnt aware of a defacto standard one. if there is one, i'd love to see it.
For me, left foot braking at speed is about vehicle rotation.
Using the technique helps me brake later too.
Left foot brake to set the front end, turn in and be done braking before the apex, back on the gas just before apex, ass end comes around and throttle modulation to get out of the corner as fast as possible.
At speed, I basically am using the brake to increase front-end traction and steering response as-needed.
I also use the technique to get the suspension as close to where i'm gonna need it (travel-wise) for an obstacle.
Well that and doing normal things, like stopping.
You're using the technique to control traction, in either case, the dynamics of what kind of traction is what changes.