You probably have heard instructors and people on TV talk about maximum width of arc in the golf swing. Well it is bad. Why is it bad? Because it requires you to stretch and pull your body out of balance. Your swing should be natural for your body.
Just because you see it on TV does not mean it is right. Attempting to get the maximum width of arc in your backswing will cause you to stretch your muscles and start to create strain in your body. Your backswing should be natural and balanced.