For a martial arts fighter who knows how to use it properly a side kick is a fearsome weapon. It can be fast and deep (in penetrative side kicks that generate a lot of power) or fast but light (used to check an opponent or stop-kick an incoming attack). By placing the body, turned to the side a side kick offers a handy attack or a counter-attack while minimizing the exposed areas of the body that can be attacked in turn. A side kick uses some major muscle groups so in order for it to be fast there has to be a lot of practice. The Side Kicks practice workout is designed to help you there.
Extra Credit: 30 seconds rest between sets.