Its origine comes from ancient Greece. They needed a way to confine their skills during training. This was first introduced in Japan. To train the techniques of the legs in Kyokushinkai Karate the arms of a karateka were bound to his back. Although this seems brutal it's a fact that in combat the fight is less harmful to the bodies.
Most damage is done by punches repeatedly on the head.
The boundkickboxer will less often be able to kick as high as the head of his opponent and probably not with the same speed and power than he was able to when he could have used his arms. If a fighter is held under water for more then 30 seconds he has lost the fight. Boys as well as playful adults love this as a sportive play. Bodies are rubbed in with olive oil which results in a need for more muscle power to hold on the body of the opponent. Traditionally done on the grass.