The World Wide Web is changing forms and screens, it is no longer a property of the desktop or even a laptop, its presence is on smaller screens like phones, tablets and who knows might spread its wings to palmtops and watches. Thus, the need to build Responsive web design for websites.
A Responsive website automatically adapts to the screens and formats of different devices. For example a mobile friendly website would completely fit on the screens of the mobile phone without compromising on its features. Building a responsive website is a better option financially than building a separate website for each device altogether.
Responsive website has become synonymous with having better SEO rankings on Google. Google places these websites on higher rankings thus they are also a better choice from an a SEO perspective. Source says that Google prefers responsive design for websites because of the fluid, proportion-based grids, flexible images and varying CSS style rules to deliver different user experiences to desktop, tablet and mobile devices while maintaining the same HTML and URL structure.
Since these websites are built keeping in mind the existing devices that they will be used on, responsive websites are extremely user friendly and preferred by majority of individuals and businesses.
Source : http://searchengineland.com/responsive-design-ranking-factor-228464