Practice swings can help reinforce sound golf swing fundamentals and mechanics. Making practice swings can also get you into positions that you may not otherwise be able to get into when you swing at a ball full speed.
According to studies, the body will adapt to the specific demands that are placed on it. There is something called the ‘Principle of Specificity’ (reference NASM). The principle states that the body will adapt to the specific demands that are placed on it or the body will get better at what is is repeatedly asked to do.
Making practice swings instead of hitting balls is a better way to improve your swing technique. If you are trying to learn the swing or make a swing change, rehearsing the move without hitting a ball will assure that you are actually doing the correct move. Repeating the motion that you want to achieve will help ingrain the move into your real swing.