This predisposition is often called dominance. One hand is dominant over the other. The same is true in the energy world. You will have one hand, or sometimes one entire side of your body that is more sensitive, or stronger than the other side. In metaphysical healing terms, many people call this your "power" side or "power hand".
As you learn to utilise energy, you build up something like a tolerance to the different levels that can be guided from the Divine, through you and into a client. The more you practice, the more you learn, the more energy you can channel during a healing session.
But even with all this practice, one hand might be able to channel more energy than the other. That same hand will also be the one that is often more sensitive to feeling energy in someone else's body. That's great for helping you to discover the location of illness or weakness in your client.