[gekko]

You're not missing anything, it's just for visual effect. The art department has the responsibility for how the game looks, and for whatever reason they wanted a film grain effect. The designers could fight against it, but it doesn't hinder the gameplay in any way. The programmers could fight it, but film grain is a really cheap effect and trust me, there would be bigger fish to fry. So the artists get what they want. But obviously not everyone liked it, since they added it to the options menu.