Running a game in a window reduces the stress that the game puts on a low end system, enabling it to run, at least to some extent, when otherwise it cannot.
nVIDIA's mobile video devices have innumerable problems of all kinds, they are unreliable and unstable, and will ignore the control panel settings quite often. Certain of them have been much worse than others. The 660s, 760s, and 860s of Optimus cards are apparently the most faulty of all in that regard, and required considerable work on the drivers to overcome the defects.
