Clear lenses are just for the most basic vision. I personally like them.
Yellow lenses are good for lower light or somewhere with a lot of visual noise (like in the woods or a speedball field at the edge of the woods). Kinda hard to explain it, but everything is just more defined.
A smoke or mirror lens is like having sunglasses, it'll darken everything for you but using them in low light will be a *****.
You may call it fat, I call it bounce padding.