Simply put... this style uses no images the default style would. The entire XenForo sprite, node icons, logo(optional text logo), and image gradients have been removed and replaced with font awesome. Removed in the sense the CSS has been deleted completely so there's no loading them what so ever.
Main points of the style...
100% Retina friendly
Easy to change colors
Global border radius adjustment(covers most areas)
Global text size adjustment(covers most areas)
Ability to host Font Awesome locally/CDN
Google Web Fonts supported(setup as default)
Easily change some of the primary font awesome icons