TL;DR: Developers of graphical user environments like Ubuntu Unity will gain the ability to deliver smooth, fluid experiences via the 3D compositor; application

TL;DR: Developers of graphical user environments like Ubuntu Unity will gain the ability to deliver smooth, fluid experiences via the 3D compositor; application developers will gain the freedom to do whatever they want with their applications' graphics buffers, because the compositor will be seamlessly combining all buffers on screen.