Have you wanted to brand your OSX machines for your end user experience, but still let the end user be able to customize their wallpaper? In OSX Yosemite (10.10.*), this is pretty simple to accomplish.
All new users (or if you wipe accounts at logout), will now use the image you placed here as the default wallpaper when logging in. At least until Apple decides to change the default wallpaper location, or replace your image.
The benefit of using this method rather than MCX/MDM, is that the end user can still customize the wallpaper to their liking, while you still get to put some branding in right out of the box.