When you're developing characters and props for games, you might have a low resolution version of a character and a high resolution version (object or group) of the same character.
The Ultimapper property uses RenderMap to bake various attributes of the high resolution source — such as normals, surface color, ambient occlusion, and so on — into maps that can be applied to the low-resolution destination object. You can then apply these maps to the destination object via a mental ray or realtime-shader render tree and preview them in a viewport.
This is ideal for game development, where a quick and easy way to transfer high levels of surface detail (color, bump, and so on) onto a low-polygon, game-friendly object is often required.