Today, visitors to a website or app may do so on any number of devices. We are no longer restricted to desktop computers. And so designers need to ensure their designs display correctly on any screen size. But how do you do this when each monitor is a different size, and new mobile phones with new screen sizes come out every year? You can't design an unlimited number of versions of your website or app for every potential screen size. This is where responsive design comes in.
By ensuring the layout, grids, images, etc., are all flexible and automatically shrink and stretch as the screen size changes, designers and developers only need to manage one design. Good responsive design also takes into account screen resolution and orientation.
Having one design with fluid grids and flexible images reduces development time and costs, allows for a uniform design across devices and platforms, and has the knock-on effect of promoting minimalistic designs which are typically better for user experience. Some designers believe that working with a “mobile-first” approach and scaling up designs for larger screens can make the process easier than having to scale designs down from desktop to the much smaller screen of a mobile phone.