Always wondered what this hack does

Ok, just a question, I have always seen this feature in many hacks called "No Fog" what exactly is it's purpose? I mean I never understood what it does. Anyone mind telling me?

likke in snow valley..it removes the fog=easier to see
thank + rep me please

From what i have seen all it does ,is makes the map you are in clear

go in snow valley match. Turn nofog on and off look in the sky.