Two for the price of one – the dual power of leg locks from bottom position: When an opponent is in your guard his legs are his base of support. If you attack his upper body with submission holds he still initially has his legs under him giving him a stable base from which to defend himself. When you attack the legs with submission holds something interesting happens. Now you are attacking two things at once – his leg as a submission target and his base of support. It is so much harder to defend a lock when you are unstable. This usually forces the opponent to change his posture to sitting or kneeling to gain a new stable posture from which to defend his legs – and this immediately renders him vulnerable to follow up positional attacks. By attacking the legs you create an automatic double attack and a follow on attack that is extremely difficult to deal with when done well and which keeps an opponent on the defensive. Make sure you can threaten your opponents legs from bottom position – you'll get twice the bang for the buck
