Well considering fogs are designed to light up only 10ft in front and to the sides of the car you would have to be traveling very slowly for them to add anything. They basically point down which is why, on wet roads, the light causes glare.
I do a lot of night time driving and there's a lot of chavs round here who think it looks cool, after a while you feel like taking a hammer to their fogs . BTW I'm not saying anyone who drives with fogs on is a chav I'm a bit more careful with my generalisations