Tripping and locking of the legs is applied when kicking and wrestling. If applied properly the opponent will trip up and fall to the ground.
Combining tripping and locking with other techniques such as wrestling and throwing, unbalances an opponent before dominating them with a throw. Tripping is even used as a counter measure to an opponent having kicked.
Tripping and locking of the legs requires good timing and understanding of foot placement and stance. When these are understood, even big men may be felled with ease.