The light might shine through to the other side of the wall as well (depending on the shaders you're using, as well as the rendering path, your shadow settings, the type of light you're using, and the type of projection your camera is using). Normally you would tweak all of these things in order to stop lights from going through walls.
What I'm wondering, though, is whether the fog can be used to do the same thing, given that it can be used to cover things that are out of the character's line of sight. This might be useful in some contexts (e.g., if you don't want to use shadows in your scene, but you also don't want lights to go through walls), and it would free up a number of other things (e.g., not forcing you to use a perspective camera or fullforwardshadows).
So what you mentioned about the MP game is on the right track, but you can't use FOW Renderers to block the effect of lights on, say, a floor (some parts of the light on the floor are visible to the character, while other parts aren't). With the floor example, I don't think switching off the renderer will work.
