Responsive design was introduced to help designers build one site on one domain that responds to a users viewport. The two necessary elements for a responsive design are a meta viewport tag to disable scaling and media queries to alter the design of the page gets smaller. Responsive design is a lot less expensive and easier to maintain than the other mobile strategies. This has added to its rapid growth and adoption.
A big challenge with responsive design is finding a balance between the content needs for both mobile and desktop. A desktop site has a lot of visual real estate that is often filled with carousels, videos, large parallax background images, and large blocks of text.If you load a feature-rich website on a mobile device you often increase the page load for mobile visitors. This is due to the large images and videos which are scaled down to mobile.
End-users don’t care about your responsive web or your separate sites, they just want to be able to get stuff done.
― Brad Frost, author of Atomic Design