Since the smart devices era and universalization, website needs to be fulfilled the convenience of reading / surfing. Your customer not only will use traditional computer to view your website info, they will probably use tablets, or even smartphones to surf it. Thus, website need to fulfil at least 3 aspects, that’s computer view, tablet view and smartphone view.
Responsive web design has become more important as the amount of mobile traffic now accounts for more than half of total internet traffic. Therefore, Google announced Mobilegeddon (April 21, 2015) and started to boost the ratings of sites that are mobile friendly if the search was made from a mobile device. This has the net effect of penalizing sites that are not mobile friendly.