I use the lunging exercise all the time. Not just to get the energy and play out but to get the horse relaxed. I know the natural horsemanship people say lunging is mindless work. However, if you do this exercise correctly and are very specific in your actions and directions, it is a far from mindless use of time. As you watch your horse moving around you, you can see how he is tracking and moving. You can identify any stiffness, lameness or attitude issues. Even my finished horses are lunged, if only for five minutes or less. When I mount, the horse is warmed up and loose in the joints. I don’t have to spend time in the saddle getting the horse physically and mentally ready to work. I know that the horse has his mind in the right place.
Another good reason to lunge is to teach certain commands. Commands that can be learned on a lunge line include go forward, walk, trot, canter and stop the feet. Transitions between gaits such as trot to canter and trot to walk can also be taught and practiced. You can work on canter departures from a stop on a long lunge line. Lunging is also a gymnastic exercise and you can see how the horse performs various gaits and movements. You can add other training aids such as poles, to help get the horse collected and engaged.