As far as I've seen, it's purely for aesthetic purposes. Personally, I think it's an awesome idea and I'm watching with interest. If it eventually changes the basic look of everything in the game, the possiblity arrises that one could grab it, change it however one wants, and make the entire UI match... It's not a huge deal, but for those of us who are a bit obsessive about our UIs, it's a neat idea.
basically it adds a letterbox texture to the bottom of your screen similar to royalbar (iirc it uses royalbar textures) you should be able to check a screenie of royalbar at any of the major mod hosting sites