well basically laptop that have two gpu, which is integrated and dedicated will work separately. integrated gpu used the most when you are not playing game, it could probably run at some app using dedicated gpu if you choose it to run using it, but when you are playing games with dedicated gpu, your dedicated gpu will do it jobs and your integrated gpu only steadying. well if you have problem with low fps, try to check your graphic card driver, tweaking the setting, my laptop also using 940mx 2gb gddr5, the fps is not really high in some games, but after i tweak the setting, the fps increasing so much(depends on the game), i could get around 70-100 fps in csgo high settings, 40-60 fps in gta 4 high settings, 27-60 fps in far cry 3 high-ultra mixed settings, 60 fps left 4 dead 2 high settings. but however your fps in games also depending on other component like ram & processor