Responsive websites - or websites that 'respond' to the size and usability of the device from which they are accessed – provide an optimal user experience, cross device. While search engines, such as Google, support mobile version websites, it is clear that responsive design is the way of the future. The flexibility and efficiency of a responsive web design gives you the power to adapt to how more and more viewers are interacting with your website while saving on long-term development costs. Some reasons to pick responsive over other options include:

Content Accessed From a Single URL
Site redirection can be confusing for both browsers and users. A responsive website makes content seamlessly accessible from a single URL no matter the device, so that users can easily share the link with no problem. Sites with a responsive design are also a smart decision for SEO, as it’s easier for Google’s algorithm to match content across devices via a single URL.

Sites Load Faster When They Are Responsive
A rapid load time is critical for user enjoyment and is now a factor in how your site is ranked by search engines. Because no redirection is needed with a responsive site, load times are reduced – and you can rest assured that users are pointed to the right version of your site.

Long-Term Cost Effective
A responsive design makes it so that there is only one version of your website needed, so you can save cost and time trying to produce an additional mobile site for devices such as iPads, cell phones, and e-readers. Plus, because there is only one version of the site, maintenance is much easier and more effective. Another bonus is that this type of site saves resources for both your site and search engine’s crawlers because they eliminate duplicate content across devices, improving crawling efficiency that can help Google index more of the site's contents and keep it appropriately fresh. Although initial costs of a responsive site may be higher than a traditional site, you get a better return on your investment.

Great Strategy for All Sites
No matter how large or small your website, it’s important to make sure that it can be easily indexed by Google, interacts well with users, is easily sharable, and overall easy to maintain. A responsive site design is essential for this type of usability optimization.

Source: https://developers.google.com/webmasters/smartphone-sites/details