I'm with Richard on this one.
The reaon for NOT using them when it is not foggy is because of safety - for all involved.
Just because many people do use them (for show?), and even if they do light up a bit to the side that does not mean you should use them.
Those lights are mounted close to the road - in order to get under the fog and thus light the road surface. But that also means they reflect much more from the road surface - and into the eyes of oncoming drivers - especially if the road is wet and there is no fog to dispurse the light.
For drivers with older eyes (ie anyone over 45-50) the glare can be much worse - and it can reflect backj upward a long way forward - further than the headlights due to different angles with the road.
And - unless you are going very slowly (under say 30MPH) the light from the fogs is so limited in distance that it provides no useful light to prevent hitting anything. It is meant for dense fog.
So running your fogs on all the time is not doing anyone any favours - and drivers who know better tend to have a very low impression of anyone who does.