I tried driving with fog and headlights on whilst going down a lonely, unlit country road at night and TBH it gave sweet FA in terms of extra illumination. I think the grass banks on either side might have been more prominent but nothing in terms of forward throw.
That is the whole point of front fogs - they are not meant to illuminate far into the distance, or even middle distance which dipped headlamps illuminate - when it is foggy, you should be travelling at a noticeably lower speed than you would on the same stretch of road in clear visibility. The whole idea of front fogs is that they provide a very low, but very wide beam - which is meant to highlight kerbs and verges. When you drive in thick fog (especially when you arn't in a queue of traffic) - you often have to 'navigate' by following the nearside kerbs, verges, hedges etc - and a properly designed, properly set up front fog will do this just fine.
Driving with only fogs on must give horrendous illumination.
You should never use front fogs alone when it is dark. If it is daytime, that is the only time they should be used in isolation.
The other thing I hate is when they have one light that's not working and the other light seems to be much brighter - almost full headbeam strength.
Hmmmm . . . I think I know why - when you 'notice' a car coming towards you with headlights that arn't correct (a bulb out, incorrectly aligned) - then we all have a tendancy to actually stare and focus on said dodgy lighting (rather than looking at the road ahead). We may not actully be aware we are doing it, but it does happen (I think the TRL did a study about 30 years ago on this - sort of the time when halogen bulbs started replacing old skool tungsten bulbs - and the whingers started to complain that halogen bulbs were dangerous). Anyway, advanced driving instructors will (should) tell you when this scenario occurs, then you actively need to focus your eyesight on your left kerb/verge (obviously at a distance appropriate to see for your speed being travelled). It really does work - and if you try it, you should notice it is much less irritating.