In my opinion it's very important.
Try this simple exercise.
With both eyes open focus on an object, now point it with your finger, be shore that you have both eyes open and you are pointing it like you're giving a shot.
OK, now close one of the eyes and then the other.
You will see that with one eye you're still pointing it and with the other don't.
The eye that is still pointing it’s your dominant eye.
Flying you must have both eyes open, so if you point your camera with the wrong eye your video might be out of range.
If didn't understand something please ask.