the only one I know actually doing that is my wife...and I dont like to ride with her...(she started doing it as a teenager,thinking that otherwise her calves would be different sizes!!! )LOL.
As far as Im` concerned, learning this long ago,its supposedly dangerous....
BUT, many race car drivers do this....
only time I had my left foot working in an automatic was when I had had surgery on my right...I used ONLY the left foot...right was over the 'hump' into passengers area...
I can sometimes , ...if I`m ready for a fast take off "hold" the car with the brake with the left foot after I stopped ,so the right is ready for 'take off'...LOL
I learned to drive with stick....and I still think the left is for the clutch...
I had a few situations when I was in my young 20`s and drove a cab (A Mercedes Benz 200D auto) and had my own car (Fiat 1500 vert stick)usually when tired and had driven 8-10 hrs in the MB...switch car, get to the first stop light and wonder why the car starts shaking ,before it stops...."oh yes, CLUTCH" save it.....
and the opposite...first light with the MB after using MY car a long time...hit brake, slow down , then other foot on (thinking clutch)hits same brake , HARD stop! LOL