I have found them very effective in heavy snow, but just using parking lights in heavy snow works pretty good also.

I have no idea how they work in heavy fog, but for heavy snow or even misty rain, I have found them to be a benefit.

I also like the fact that other drives will probably be able to see me better if I have the fog lights on.

 

I'd probably agree on everything except using parking lights while driving. I've seen so many people driving around with just their parking lights on in fog or whatever and I've got to tell you... I see them LONG before I see their dim amber parking lamps. They aren't called driving lamps after all. Its not just how far you can see... its how far you can be SEEN as well.

 

I think there are different kinds of fog!

In the great white north, we have very cold ground temperatures.
Usually when a warmer air mass blows over snow covererd ground, you get dense ground fog, almost like dry ice fog used as haunted house effects. This may only be a few feet thick. Last night in fact, I could see the moon, but I could not see two white dashes on the road ahead through the fog! Here, the fog lamps only blind you... making it harder to see down the road.

However, coastal fog ( which I'm not in ) is probably a different story.
That fog may be less dense very close to the ground.

 

You are right TeeSter, driving with Parking Lights only is NOT a good idea, but sometimes with headlights you can't see much at all.

Fog lamps are the best choice in foggy and snowy weather.

 

My fogs work well here in So Cal. We often have pockets of thick night time fog here this time of year. I have had fog lights on many cars over the last 40 years. These work as well as any. Yellow may be a little better as the glare is lower. But, you get glare anyway since the headlights are on.

I do not use my fogs to drive faster in fog, I use them to drive safer in fog.