I shoot the same way I shoot real steel.
both eyes open, its an easy, relaxed way to shoot. one eye means your forcing the other closed....not to mention depth perception and view range.
picture in a picture
being able to focus through your optics on a small area while still being able to keep focus with the other eye on your periferal(sp).
Deer hunting, always use both eye. for a moving target, lead, watch it with both and as it drifts into focus with your shooting eye in the optics, all is well, while keeping view of the surrondings.
heck, best way to describ it is the old Delta Force games.
though in hardcore airsoft combat, with the low fps and terrible accuracy, optics arnt always needed. aiming with a stream of BBs works too.