From a track-day/road-racing background I find LFB most useful for settling the car in precarious brake-throttle transition points. The turn-in for the carousel at Sears Point or the turn-in for the corkscrew at Laguna. Not necessary but when the tires are hot and slippery LFB helps keep things smooth.

As for "heel-toe" I recommend everyone buy "Going Faster" by Carl Lopez and learn the Skip Barber technique (it's bascially ball of foot on brake, roll foot over to blip throttle - works in just about every car where the pedals are close enough).

 

I tried LFB at our last auto-x, for the first time in competition. I ended up doing something like what Kevin S describes - LFB while still on the throttle, switch to RFB/Heel-toe downshift, then on the throttle with just a little dab of LFB to rotate the car. I was giggling like a schoolgirl. Unfortunately, I was on a completely inappropriate tire and still got my butt kicked. I'll be ready for the next event though.