Well…. if you want a background image/color on the full page, and the contents have a fixed/maximum width and need to be centered, then you’d need a wrapper: http://codepen.io/anon/pen/dbutk
Even though, technically you could just set the background on the HTML element and then center/space the BODY. So then you wouldn’t need one: http://codepen.io/anon/pen/dKEiB
But then the idea is the same.