If your website is optimized for mobile devices, Google will prioritize your website in search results, for users searching for you from another mobile device. Sign-up for a BuzzPage (optimized for mobile devices) and get a higher priority in search results, and have a much better viewing experience on more devices.
Starting April 21, 2015, Google Search will be expanding its use of mobile-friendliness as a ranking signal. This change will affect mobile searches in all languages worldwide and will have a significant impact in Google Search results. Users will find it easier to get relevant, high quality search results optimized for their devices.
(Source: Google Support at http://support.google.com/adsense/answer/6196932)
Google provides a tool test your website’s mobile friendliness: