I'll dip into the waters here.
I rarely use my fog lights...generally only when it is foggy. When it is snowing, depending on the size and density of the snowflakes, I might also use the fog lights. If I need more light under clear weather conditions, I use the high beams. If there is an approaching car, or I approach another vehicle from their rear, only my low beams are kept on.
Turning the fog lights on does add to light pollution for other drivers. If it didn't, they could not determine that the fog lights were energized on your vehicle. Even when properly adjusted so the majority of the light is toward the ground immediately in front of and to the side of your vehicle, any surface film or dirt on the fog light polycarbonate covers or glass lenses, or the design of the light projection system itself, will disperse light elsewhere. I personally find it very irritating when a vehicle behind me has their factory installed fog lights turned on. The dispersed light from the fog lights is often greater than that from the main low beam headlights.
I wear glasses, and unfortunately even with anti-reflective and non-dispersal coatings, surface scratches and always present film and dirt on the lenses further disperses the semi-collimated illumination such as that from headlights and fog lights. Light from point sources causes dispersion even within the eye, or just on the surface of the eye.
As I've aged, the use of fog lights is even more important for my needs. But I also recognize that other people are distracted by the same light sources I use to guide me. It's my decision to help less capable drivers prevent an accident.
BTW...an interesting corollary:
The night I bought a new 2000 Audi A6 with HID xenons, after I had driven only three blocks from taking delivery at the dealer, I came to a stoplight on a well lit street. As I waited for the light to turn green, a cop on his beat approached my car from the side. He tapped on the window and asked me to roll it down. At that point he told me to turn on the headlights. He had assumed the headlights were off, most certainly because the wrap around headlight lenses were so new and clean that no light dispersion was evident. I told him the lights were, in fact, turned on. He was shocked to see the projection light system was on when he went to the front of the car. His knee caps were brilliantly illuminated.
Of course, in a relatively short time the polycarbonate headlight covers accumulated surface defects. Now, even with the headlights clean of film and dirt, there is enough light dispersion to easily determine they are turned on from the side of the vehicle.
