I love the idea of switchable graphics and when Nvidia began doing it I thought they had struck gold. Why is switchable graphics important? It allows both battery saving and a performance mode.
Battery Saving Mode
By enabling the integrated graphics you can add a lot of hours to your system. If you are a mobile user and need long periods of battery life this is key.
When you need to do something intensive like rendering video, or playing 3D games the discrete graphics can help you have a smooth experience.
HP DV6T QE
With this HP laptop you have the option of having everything running either on Intel HD graphics, or discrete AMD graphics. As you can see on the videos the screen flickers when switching modes. If you are running certain programs it might give you a blue screen, so make sure to quit programs before doing that.
There are different ways of switching modes. Usually you can right click on the desktop and click on "Configure Switchable Graphics" and then assign the GPU. Another method is by unplugging the power source.
Lenovo ThinkPad W520
The Lenovo system allows the all Intel HD graphics, all discrete Nvidia graphics, or both at the same time. I think their technology is ahead of AMD's. There's a slight flicker and the graphics mode change. By default the system has an "auto-select" mode which tries to determine which graphics to use for that application. The first time you run something 3D it might not work, but the second time it will.
You can customize the modes by accessing the Nvidia Control Panel. Again just right click on the desktop and you should see it.
Switchable graphics rule and Nvidia's Optimus Technology is a much more seamless experience.