1. Mobile websites have more usability concerns (this is mostly due to the lack of screen real estate), so it’s practical and more efficient for the primary focus to be on mobile design.
2. It’s easier to scale up the mobile version than it is to scale down the desktop version (again, because of the lack of space on mobile websites).
3. Mobile-first web design helps to reevaluate what’s visually and functionally necessary.

Take Advantage of Mobile Devices’ Native Hardware

Mobile hardware (like the device camera, or GPS services) isn’t specifically reserved for native apps, and as mentioned earlier, responsive web design isn’t just about “making everything fit.” It’s also about adapting to the capabilities of the device. In the case of mobile web design, since mobile devices have easy to use cameras, some micro interactions—such as data input—are actually easier on smaller screens as long as websites are taking advantage of the available native hardware.