Each opening-closing cycle causes a small amount of wear to the jointing (you could acutally wear a gun off-face without ever firing it). Each barrel firing causes a small amount of wear to the jointing and to the respective lock.. So, you will experience opening-closing wear and right side wear each time you fire the gun. However, not firing the left barrel does not cause some kind of wear imbalance. Your ritht lock will show more wear to levers and springs than the left, however.