Zooming in makes you see less which in turn means less processes or actions need to take place within the game. It's an old school trick for older flash games to play Zoomed in to achieve the same thing.
However, I toggle zoom view in and out like a crazy person hot keyed to my left trigger on my Xbox 360 controller, used in conjunction with my keyboard/mouse. For some reason, when in FS mode that function no longer works.