With more people browsing the internet on the go using a mobile device than on a computer, making sure a website looks great and works on a mobile should now be prioritised over designing for use on a computer. The approach for many years has been to create one version of a website developed to work on desktop computers and tablets, and a separate "mobile" website that is just for mobiles. For some companies, having a seperate mobile site is necessary, such as for Amazon who's desktop website is too complex and would have to be too radically changed to be adapted for mobile.
However, for most companies and people, a responsive website is both ideal and cost effective compared to having two versions of your website developed for both computers and mobiles. I develop a website that automatically works on all devices and browsers. A key factor when ensuring a website is mobile friendly is to ensure the website loads quickly. With expertise in image optimisation, page delivery and site structure, websites I develop load extremely fast regardless of device or browser.