This is the so called Optimus technology by Nvidia. They made it, to increase battery-power time for laptops. What first sounds good, is sadly very awful when it comes to certain things, like hacking the display drivers to output 15khz resolutions for example. You will not be able to do that, because you share your display-output with the integrated Intel graphics and everything is outputted through this Intel graphics port. Dedicated Nvidia cards in laptops, without Optimus technology, dont have that problem. I regret it so much, that i had bought my laptop with Optimus technology.
... and yep, you can only choose which graphic processor is used through the Nvidia panel. I wouldnt advice to use the Nvidia processor all the time for everything (at least if you use the laptop in mobile mode), as you will not have any advantage from the Optimus technology at all and shorten batterypower time.