Myth - You must hit your groundstrokes with a closed stance (body sideways to the net).
Truth - You do not have to hit all of your shots with a closed stance. The pros hit with an open stance (body facing the net) on most of their forehands and sometimes on their backhands. The bottom line is this. Hit the way that feels comfortable and natural to you. A closed stance is not superior to an open stance. In fact, the open stance has more benefits than the closed stance. Some benefits are listed below.
1. When you are finished hitting with an open stance it is much easier to recover back to the center of the court because your body has not moved as far away from the correct recovery position as you would have when hitting with the closed stance.
2. You can generate more power in the open stance because of the coil and uncoiling affect of the body, along with the ease of swinging upward in this position.
3. It is easier to regain your balance in the open stance. In the closed stance you turn your whole body completely sideways, making it more difficult to recover your balance after the hit.
The open stance is an excellent, relaxed, natural shot, especially on the forehand. When hitting forehands with the closed stance the arm is behind you. This makes it a more difficult shot to time correctly because your arm is farther away from the ball. Hitting with an open stance brings the arm closer to the oncoming ball.
Now, I am not telling you to never hit with a closed stance. Use whatever comes natural on a given shot. The point is to not fit yourself into a rigid mold. When playing tennis you should do what is best for the situation at hand. Sometimes the situation calls for an open stance and sometimes a closed stance. Practice letting this happen naturally and you will be surprised how your body will figure out the right way to hit the ball.
You will develop spontaneity through preparation!