Nvidia Optimus, as it comes, does switch automatically, but one can go into Nvidia control panel and select to use the Nvidia card for each particular program.
I have tried this with Photoshop in past, and unless one is doing 3D rendering, Nvidia card does not speed things up for usual 2D photo editing. Using the Nvidia card does make the laptop run hotter, resulting in the fan kicking in faster and louder
Yes and No, there are some misunderstandings about Optimus. The application or game is recognized by the nvidia software/profiles, and switch to the recommended GPU, but it stays
on that GPU until you exit your application.
For example: You start up your computer and the Windows GUI is always using your onboard (intel) GPU! When you decided to start an application or game, and that's were it wil switch to the recommende/preferred GPU when the program is recognized (profiles). When you exit the application or game optimus switch automatically (there you have it!) back to your onboard GPU. Try to run WEI (Windows Experiance Index) it would allways run on your onboard GPU.
Photoshop CS6 and CC does benefit from the much stronger nvidia GPU against the onboard intel. True you won't notice it when painting or fill a color, but more and more actions or plugin's use complex maths (OpenGL/OpenCL/Cuda) and that is were the nvidia GPU really shines!
I hope this clears it up for you... It does not
change dynamically/automatically between your onboard or dedicated GPU while in
your application or game.