For example, simply add a layer, and rotate the spine forward at any frame, and a run cycle becomes a crouched run. The original biped motion is kept intact, and can be viewed by switching back to the original layer. Layers can be viewed individually, or as a composite of all the animation in all the Layers. Layers behave like a : the biped can adopt any position.
Layers allow you to easily adjust raw motion capture data containing keys at every frame. Simply add a layer, and keyframe the biped. You can also use layers to change the global position of the biped in a freeform or footsteps animation by adding a layer and moving the center of mass.