Google Webmaster Trends Analyst John Mueller tweeted that the boost it earlier posted about favoring mobile-friendly sites is now live for all search results. If your site is not mobile-friendly you will see your Google search referrals go down and if your site works great in all mobile devices you should see some improvement. In essence, if two sites are equally targeted to be a top search result for a given query the site that is the most mobile friendly will show up while the other site will move down the list.
FYI The mobile changes mentioned here are now fully rolled out. https://t.co/fTB3ia6LJ2
— John Mueller (@JohnMu) May 12, 2016
Google recommends that you check your site with its Mobile-Friendly Test tool. You can also read Google’s Webmaster Mobile Guide for more information.