Prime example: I see a moto 360 and want to use the face. Most of the time the moto watchfaces do not have an ambient/dimmed mode so I normally "add" that layer by duplicating layers to show in dimmed only. If I could select multiple ones and do a mass edit of just basic features like show in ambient mode only.
And the reverse would be similar if a person with a moto 360 wanted to use a face made for a GWR.