With the Euro light switch you can run fogs without headlights. Otherwise, I think the fogs are useless considering the brightness of the headlights. I see so many cars with their fogs and headlights blazing and I do start to wonder why. I always thought of the fogs as something to get under the fog and avoid the reflected light from the headlights. With both fogs and headlights, there really is no advantage. In fact, it may make the reflection even worse.
With my old Mercedes, the fogs did tend to add a wider beam to the less than stellar headlights on low beam. With the newer brighter headlights, however, it seems the fogs really are just a toy and can also be annoying to the other people on the road. For me, other people's fogs seem to add glare to oncoming cars and cars following too close behind me.
I only use mine before I really need headlights, like a driving light or DRL in less than ideal lighting conditions in the morning or early evening. I don't use the fogs when the headlights are on.