Use LFB in sim rig when using paddle shifters or sequential shifter, but RFB when using gated shifter and clutch, but in my own real cars, I always RFB.
I tried LFB and it feels bizarre in a real car, but I am sure I could do it in a real car with paddle shifters easily. The problem with LFB in a real car is that you'd tend to rest your foot on the brake and constantly wear down your brake pads and rotors. On a race track I guess that wouldn't be as much of an issue.
I do sometimes see morons cruising down the highway at 65MPH with their brake lights on though, and I know they are left foot braking, and they are usually 85+ years old. As I go by I always check their front wheels and sure enough, they are always black with caked on brake dust..