Tournament locks prevent the Polar Stars (electro-pneumatic) rifles from increasing their fps (regulated gas flow adjustment) while on the field. Without it, they could chrono at 300 fps, and adjust while in play to 410 or so. With their rounds per second, that could easily become a wall of plastic pain, not to mention dangerous.
As long as your using an AEG, you will not need one. The main way to increase your fps is by changing a spring which requires too much time and effort to effectively adjust while in play.