Responsive design is vital to give your users a great experience regardless of them using a smartphone, tablet or laptop. Take a look at this site on a smart phone then on your desktop, you will see the design morphs to fit the device you are using.
Google has said by the end of 2015 they expect more users to be online via smartphones than desktops. Its vital you start looking at making your site mobile responsive. In the near future Google has said it will rank sites that have a mobile version higher for searches performed from a mobile device. So if you do not adapt soon you will miss out on all those searches.
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