Optimus technology, we discussed it earlier on. One of the things we didn't know yet is that Optimus enables you to pull discrete graphics cards out of a running notebook, and put them back in later when you need some more power for a graphics-intensive application. This works because Optimus electrically shuts off components in your notebook:

The benefit of electrically shutting off components in your notebook, including the GPU, is that it extends battery life. Compared to a standard notebook with a discrete GPU Optimus can extend battery life up to 2x*. The benefit of immediately turning it on again is, of course, that you get all the graphics and processing capabilities of the GPU at a moment