The mobile theme is a stripped down version of the site, which includes only the basic site content, nothing extra. It’s designed for use with non-responsive themes, as a fallback so that key site content is readable.
Since Gridspace is already responsive – adjusting automatically to screens of different sizes – the mobile theme isn’t necessary and I’d recommend keeping it turned off. That presents a site to your mobile users which better matches the look and feel of your desktop site, and more content is accessible as well.
You can learn more about responsive themes and the mobile theme here: