One of the things we're supposed to do when we're shooting is keep both eyes open; That helps avoid fatigue from shooting for hours, but also lets us see what is going on around us. That is smart in case good action is happening to the side. It's also good because you might need to be aware of an unsafe condition unfolding while you're shooting.
I've noticed that my eyes go a bit wonky after shooting with only one open, so this is an interesting idea. I'd never heard of it until now.
My main question is: how do you train yourself to do it?
Also: are there any other advantages? How prevalent is this among photographers?