When you add a new layer, every bone gets that new layer, and you can choose the parts of the CATRig that you do not wish to use the new layer. This process is called feathered weighting. Feathered weighting is achieved by editing the local weights of individual rig elements.
Example: To turn down the weight on the left arm only (feathering layer weights):
The arm is no longer be affected by the current layer.
