"Many years ago I had a really crappy car. It was automatic transmission but it had no 'choke'. So until it was well warmed up, if I came to a complete stop, it would stall. Since I hated waiting very long for it to warm up, I would just go, and if I hit a red light, I'd shift it into neutral and gas the engine to keep from stalling."
Of course, then the question becomes, why didn't you just gas the car at the stop light without bothering the shifter? An automatic transmission will let the engine spin under power and the brakes will keep the car still. It's not delightful for the transmission, but since it was "a really crappy car" I can't say I'd brook too much concern for it in your shoes.
As a general rule, shifting an automatic transmission isn't necessary and it's not a good idea to put it out of gear in an emergency situation because it's just something else you'd be devoting attention to when you really need to devote attention elsewhere.