I'm quothing this from the paper that I got with it.
" The balance Training Advanced System is best for use at the trot and canter. At the trot, this training system concentrates on building muscles in the back and neck while also achieving flexion. At the canter, the system begins teaching your horse better balance by bringing his hindquarters under him. By transferring his weight from the front to the rear, the horse is able to balance and propel more easily"
So basically it helps teach the horse to engage his hindquarters, build a topline and muscles, and to move away from pressure (if the horse raises his head, there's pressure on the bit, and as soon as his head drops back down, the pressure is released.