If you've ever been unlucky enough to go jogging, you'll know that it is easier to run at your own speed than try to keep pace with a friend. You can settle into a rhythm, relax your body and ward off that exhaustion for longer.

Your horse also has a natural rhythm in each gait in which he will be more balanced and so find it easier to work. The rider's job is to find that rhythm and establish it. This isn't an easy task but, with the right tools, in particular the half halt, it is possible.
Rhythm is the best of your horse's hoof-falls - Tempo is the speed of this rhythm.
The half halt is a vital tool in establishing your horse's rhythm because it helps you to control his speed and impulsion. It allows you to collect your horse together for a second by creating energy with your legs and momentarily keeping it with your hands. A half halt also helps rebalance your horse so he is in a much better position to maintain hi rhythm. As long as your horse is going freely forwards and is obedient through transitions, he will benefit from being taught how to half halt.