I replaced two older dimmer switches for light fixtures within a double gang box with two new Lutron LED dimmers (Skylark Contour CTCL-153P-AL). Since the dimmers that were replaced had no ground wires attached to the ground wires within the gang box, I removed the ground wires from the new dimmers (since the gang box and new Lutron faceplate are non-metallic, I believe that this meets NEC code)
Upon wiring the hot side of each dimmer, I discovered that the older dimmers were attached to an additional black lead from another Romex cable within the gang box. Although I wired the new dimmers exactly like the older dimmers, I'm just curious why there would be an additional cable!
Since the Lutron faceplate is nonmetallic and noncombustible, the NEC allows for the green wire to be capped or removed from the dimmer switch (see dimmer switch highlighted notes)