User scaling is more than just the zoom gesture, it's a different way of controlling the web page in Mobile Safari, and because of these differences the user ex

User scaling is more than just the zoom gesture, it's a different way of controlling the web page in Mobile Safari, and because of these differences the user experience is quite different. With User Scaling enabled, you can use the zoom gesture, pinch gesture, or double-tap gesture to scale the viewport. But how does Mobile Safari know the difference between a single-tap and a double-tap? By waiting 300ms after the first tap to see if you tap again! By disabling user scaling, yes the zoom gesture (and pinch gesture) no longer scale the viewport, BUT Mobile Safari also stops delaying all tap input 300ms to wait for a double-tap. that means every link you tap, every button you press, every field you highlight, and every other interaction with the site goes much faster and smoother. Faster tap response time = a better user experience. Even if the site was 100% responsive, when I turn user scaling off Mobile Safari just works faster than with a fully responsive, scaled and accurately displayed site where Mobile Safari is waiting to tell single-taps from double-taps. I know for some people 300ms doesn't sound like a lot, but for us it would translate into a loss of at least $,$$$ annually if not $$,$$$ due to the loss of those mobile users due to a 'non-responsive' site in a different way: time.