What's that ?
The laptop manufacturers developed new technologies involving two graphic cards in an single computer, enabling both high performance and power saving usages. This technology is well supported on Windows but it's still quite experimental with Linux distributions.
With nVidia's Optimus, the images are always sent through the integrated Intel card, even when the computations are made on the discrete card. There's no physical switch which could allow the user to "plug" his monitor to the card of his choice. The user can't use the nVidia GPU directly, even on Windows.