I've never LFB in an automatic before, because they coast so well I usually accelerate and remove my right foot and my right foot is hovering to select more gas or brake at any moment. I can see how a hovering right foot being able to chose either output is just as good as a hovering left foot, but I don't know how someone can claim that LFB doesn't help in emergency situations. I've seen the studies, reaction time from when someone sees brakes lights in front of them, removing their right-foot from the accelerator, then applying to the brake is just about .75 - 1 seconds. That's a LOT of distance as 70MPH (77feet). We were actually studying the effect of putting a device so that when throttle input is rapidly removed, the brake lights come on, theory being that rapid throttle removal is usually followed by braking. It needed more tuning but showed great results improving reaction times by .7 seconds because people in the back saw brake lights earlier (even before braking had occured).
Anyway, based on that I can without a doubt see how when you see braking, you instantly start to apply braking with the left foot while removing throttle with the right foot. I bet you'd easily save .5-.75 seconds. There's NO WAY you can claim that using your right foot in such a situation is as fast (much less faster). As for needing to accelerate away sometimes, tell me how quickly you can choose to acclerate or brake on demand if you're using two feet? Or right, about as long as it takes neurons to fire, that's all. Very rare situation but I could easily see how that exact setup would be best for emergency swerving, brakes to slow and shift weight forward, gas, then brake and gas to rotate the car to point bake the other way. Yes, brake and gas to rotate the car, at the same time! Everything requires finesse and takes a lot of learning.
The only place I left foot brake is when racing. The main racing I've done is autocross but I've used it rallying and in gravel. It's really the only way I can get my old Quattro to rotate in turns, but more than that, the purpose is control. When you're pushed as far as suspension and traction will allow into a corner, simply lifting off the throttle too fast is enough to get the front to dive and overload the front traction and spin out. The finesse is slowly, fluidly controlling the throttle and applying just the amount of braking you need, smoothness is the key to keeping traction. It also is great for low traction conditions like ice and gravel. In my Audi I used it a bit differently, the old Quattro system puts much more power to the front wheels than the rear and in a turn if I quickly stabbed the brakes while throttling up and turned the wheel it would kick the rear out just enough, I kept traction at the front with the accelerator (shifting weight back). That car was so front heavy and liked to understeer so much it was the only way to get through corners or gravel with any kind of speed. The cool thing with Quattro is even if you're sideways or out of control (like oversteer condition), you just aim and hit the throttle and it'll go where you aim regardless of traction. Fun Fun.