Over the past year or so Google have made it their business to reward 'mobile responsive websites' with a boost to their Search Engine Results Page (SERP) position.
This is great news to all those websites out there that look as good on a mobile device as they do on a desktop. However not every site is able to dynamically change how and what it displays depending on screen size. These websites are in danger of taking a SERP position hit.
The last thing you want as a website owner is to see your site disappear from the search engine results, however if you look at it from Googles perspective you'll understand why they've taken this course of action.
'more Google searches take place on mobile devices than on computers in 10 countries including the US and Japan.' A quote taken straight from Googles blog site itself. Their customer base is using their service on mobile devices more than ever before, it's not a great customer experience if half the links they click on look rubbish on mobile devices.
So if your website isn't mobile responsive then you're living in the past and need to catch up or risk becoming obsolete (at least from Google's perspective).