When you have a huge canvas (think: responsive design) but the content you need to display is very narrow, how do you prevent it from looking awkward? Center it, left-align, find more stuff to fill the page with, etc...?
This can be a problem when trying to take advantage of your full viewport while using a common layout on each page. What if your viewport is 2000+ pixels wide and all you need to show are a few widgets or some form to fill out.
It helps to have width for displaying things like data grids, because more width means more columns you can show without scrolling. However, there are other types of UI components that don't do so well with it, like forms or copy. If you've already committed to a responsive design, how do you get these items into the page and have it look natural?