Early in 2014 a study by Comscore confirmed that more consumers are using their mobile devices to access the internet than a desktop - a trend that can't be ignored.
On April 21, 2015, Google released a new mobile-friendly ranking algorithm designed to give a boost to mobile-friendly pages in Google's mobile search results. Mobile-friendly sites are useful, intuitive, readable, and fast. They don’t require users to pinch-and-zoom, and they’re branded consistently with the company’s desktop site. Now, they also have to be recognized by Google as mobile friendly.
The idea though, is very simple: if your website isn’t deemed mobile friendly, it won’t rank as well in mobile search results.
If you have a mobile site but aren't sure if its mobile friendly, use Google’s Mobile-Friendly Test.