To “user-scalable=no” or not to “user-scalable=no” in HTML5

For responsive design, you do not have to use user-scalable=no. Use it only if you want your application to look more like a native app.

Zooming is a key feature for accessibility and you need to keep that in mind. You can control that users won't break your design if they zoom in. If you are doing responsive and your design breaks when zooming in, then you're not doing it right.

If you totally need to use it, then keep in mind that zooming is an important accessibility feature that is used by many people.