Use this option to display one wallpaper per desktop (feature available for Android 2.3 and later), so that each desktop looks differently.
When using PNG files, it is possible to create transparent areas in the image. In that case Lightning Launcher will display the system wallpaper behind. As a consequence it is possible to create stunning setup where parts of the display are transparent and let you see a live or scrolling wallpaper behind.
Important: using one wallpaper per desktop consumes a lot of memory and can slow down Lightning Launcher. Use with care.