I am learning to shoot and my instructor says that, even though I am right-handed, my left eye is dominant and that I should therefore learn to shoot from my left shoulder. Is this essential or could I shoot from my right shoulder and simply close my left eye?
You are not alone in this situation and should be grateful that your instructor has highlighted it for you. All too often people with this master eye problem are told to close one eye, but this quick-fix solution only gains results in the short term. As a shooters skill improves and targets become more difficult, progress can be hindered. Also, many people who try to change shoulder use an opposite-handed gun, hindering themselves further and developing bad technique.
It is, of course, down to the individual to decide how he or she progresses and, in some cases, shooters are content to close one eye. The most important thing is that you have been given information to enable you to make an informed decision.