If you are using one foot for braking and one for gas, there’s bound to be some overlap when your depressing both at the same time. Obviously that’s counterproductive. It’s also very hard on the brakes and the transmission.
It’s perfectly fine to drive this way if you can guarranty that you’re not hitting both at the same time. Unfortunately it’s impossible to make that guarranty, so you really shouldn’t do it.
Besides, it really doesn’t help you unless you plan on driving with your foot hovering above the brake pedal, which gets exhausting after a few moments.
It takes just as much time to lift your left foot off the floor and depress the brake as it does to lift your right foot off the gas and do so.
There’s also the matter of leverage.
If you brake the way you are supposed to, using your right foot, your left foot remains on the floor giving you a base of stability and keeps you stable. Normally, this is not a big issue, but in an emergency or a violent manuever, there are going to be considerable lateral forces throwing you forward, back or around. This makes it difficult for you to find the brake pedal, and if you do, it hampers its use as you’re recquired to use a certain amount of pressure to maintain your stability. In an emergency braking situation you are going to be thrown forward, and you need something to push against. If you are braking with your left foot. you’ll instinctively use your right foot, and more than likely stomp on the gas pedal in extremis.
Race car drivers do it with both feet because they are so tightly strapped into their cabins, that they don’t get thrown around at all. Safety restraints in passenger cars aren’t nearly so confining, so you can’t get away with it.
The only reason to do it is because it “feels” convenient and safer. It’s really not. It’s hard on the car, and you’re not nearly so effective in an emergency.
If you feel that you are stamping both pedals with your right foot, then you need to learn to move your foot over to the left more, before you hit the brakes. That’s all.
I got a book on offensive driving here somewhere. It’s for limo drivers who drive celebrities and stuff and it goes into it in great detail.
In fact, the only time you are supposed to use both feet is if you are trying to create a power slide, end even then you’re really only supposed to use one foot sideways on the pedals while you brace with the other. You only use two feet if you can’t master the manuever one-footed or aren’t wearing the right kind of footwear (which apparently is extremely important to good pedal manipulation.)
The two foot method is bad driving.