In a nutshell, a mobile-friendly design will provide mobile phone and tablet users the same, or similar, experience that desktop users receive. At 6G Web Design, we utilize responsive designs that "respond" to the width of the user's screen. We take advantage of media queries to define styles for mobile phones, tablets, and desktops. To see this in action, on your desktop or laptop, decrease the width of your browser window and watch how this page "responds".
With increasing, if not the majority, of online consumption coming from mobile devices, we encourage all of our clients to implement a mobile-friendly design.