If you recall Nvidia Optimus you'll know this is a system that allows your computer to dynamically switch between graphic cards depending on process at hand.
This time, I bring you quite a clarifying video that shows that the external - more powerful - graphic chip is completely powered off when not needed (not just in a suspended standby state.)
How can we be sure? Well... how about actually removing and re-attaching the graphic card while the rest of the system is still powered on, is that enough for you? :)
