Google notified all of the webmasters through the Webmaster Central Blog, that will start Directing smartphone users to the page they actually wanted to visit. They will start showing in search result pages that website may open the site’s home page and asking you if you really want to visit that page, that is not mobile or responsive. You will have to click on Try it anyway or learn more, to find out why this noticed appears bellow the clients url.
Google believes this update will make mobile search user way happier, since they have been landing on the pages that didn’t work on mobile device or faked mobile re-directs back to the site’s homepages.
How to Find out?
If your website has those errors you can find for yourself browsing through it with your smartphone, or you can set your browser to act like a smartphone. Webmasters will see that in their webmaster tools back-end interference.
What can You lose?
You can loose tons of mobile traffic to your website, since your website will look like its not mobile accessible and people will be less likely to click on it. If your website was not mobile friendly in the past you should see higher percentage rate in your Google Analytics mobile devices bounced rate.
Make sure your website is at least mobile friendly or responsive, best solution is to have a mobile website design just for mobile devices. You can contact a professional web design agency to help you out.
I would recommend using responsive CMS themes for developing or re-designing your websites.