I have disabled NVidia Optimus on my Dell Precision M4600 since I cant dim my screen if it is enabled for some strange reason. So, what does that actually do? Does it use the nvidia card all the time then or what?
Windows – Disabling NVidia Optimus
dell-precisionnvidia-graphics-cardoptimuswindows 7
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Short answer: It doesn't "switch" and you can't disable the Intel IGP.
Long answer: From a hardware point of view the Intel IGP is always handling image output to the laptop's LCD screen. The NVIDIA GPU copies rendered graphics into the Intel IGP's frame buffer (which resides in system memory) when it is active. The Optimus software makes certain programs use the GPU based on the loaded profiles and user settings. It currently does not support running the OS desktop compositing on the GPU.
See the Optimus White Paper for more details.
The Asus K43SJ does not use the integrated Intel HD graphics (whether it's on the CPU or not), so you're not going to be able to use Optimus.
I came to this conclusion by the fact that the Intel Graphics are mentioned nowhere on the support page for that model, and the fact that they ONLY offer the nVidia driver (where as the K53SC does provide both the Intel and nVidia drivers).
The technology is there in the nVidia card, the CPU and such, but since this was produced right in the time-frame that Optimus was starting to be implemented, I think you just got a model series (the K43) that Asus put out before they had Optimus ready (I don't believe it was introduced until the K53 series).
Best Answer
What does it do? It "intelligently" switches between the NVidia GPU and the Integrated GPU in a system. This is to save power. If you are surfing the web, reading your email, there is no need to be using the more powerful NVidia GPU. This would shorten the charge life of your battery, requiring you to recharge it sooner... if you were using it all the time for mundane tasks. Since the NVidia dedicated GPU also generates more heat, this causes your laptop to run hotter. Laptops in general have issues shedding heat in the best of circumstances, thus generating more heat when it isn't necessary is typically frowned upon... performance-wise.
Now... with Optimus running, when you play a game or use a program that requires more GPU, the dedicated NVidia GPU is turned on and you get all the joy and happiness associated with a powerful graphics processor when you need it.
Turning it off will typically disable the dedicated GPU altogether, saving battery power but making your game performance suck.