Its not a lockout its a lockup. Its not locking anything out, it locks the clutch pack up. A lockup uses centrifugal force and pushes against the pressure plate of your clutch. The faster it spins the harder it pushes against the pressure plate, putting more force against the clutch pack, which essentially locks it all together. Most are typically driven off your inner hub, which is attached to your transmission NOT your crank. So, the faster your wheels spin, the harder it locks up. There are some different types that drive off the outer hub and lock up based on engine rpm instead of wheel speed. There are also different types that offer hydraulic time delay functions and secondary lockup functions so you can custom tune the setup to lock the clutch up when you need it to. In a very generalized form, you want the clutch to slip as you come out of the hole, keeping your engine RPM's up and in the powerband, then as you start to gain speed and go through the gears the load on the clutch gets larger and the lockup starts to come into play and adds pressure to the clutch system to keep it from slipping.
-Jared