Sections are full width, however the inner container (i.e., where child elements go) has a maximum width. This is what you configure in the section itself using the “Maximum width” setting.
It’s important to note, however, that sections exist within the body of the page, which is controlled by the theme. If your theme supports full-width layouts (i.e., the full width of the browser), sections will expand to fill that entire area.
I suspect your asking whether there is an option for having sections “break out” of the content area of a theme, regardless of which theme is being used. This is currently not possible, mainly because of how “hacky” existing JavaScript and CSS approaches for achieving this are and all of the various considerations (e.g., what happens when a page has a sidebar?).
There’s certainly nothing wrong with making minor CSS changes to your theme to allow full width layouts if it doesn’t already, but changes of this sort will necessarily be theme specific.
If you’ve already found a theme that you really like, except for the fact it doesn’t support full-width layouts, get in touch and I’ll be happy to help come up with some CSS to help out.
I’ll mark this as resolved for now, but I am happy to reconsider this position if there’s sufficient demand (and a reasonable solution).
