The transition between the desktop and tiled environment in Windows 8 is a full-screen state change. Visual elements are unique to each, creating a transition that is jarring and disorienting.
As seen in this Windows 8.1 preview from Microsoft however, an incredibly simple and seemingly effective solution has been introduced; persistent wallpaper. By allowing the use of identical wallpaper in both the tiled and desktop environments, elements in each now inhabit the same virtual space suggested by the wallpaper image.
This simple change introduces a hierarchy to the OS and adds an orienting sense of depth; desktop and tiled elements alike now appear above the same wallpaper.
Of course, the preview video shows an utterly clean desktop, devoid of any icons or open windows. But nonetheless, persistent wallpaper can only be seen as a usability improvement to an inherently conflicted and complex operating system.
Source: WindowsVideos YouTube Channel