At 30mph, you are travelling at 44 feet every second. At 60mph, you are travelling at 88 feet every second.
Your foglights illuminate the road what, 10 feet in front of you? So if you do manage to miss a pothole in your headlights, perhaps becuase your eyes are firmly fixed on the road just in front of your bonnet, at 60mph you have a whole 0.1 second to either brake or steer around the pothole.
Is anyone on this forum a good enough driver to react to an obstacle and steer the car around it in a 10th of a second?
No?
What foglights do on country roads is give you a perception of increased visibility. Becuase the light directly in front of your car is brighter, your brain perceives there is more visibility. This gives you confidence and makes you do things like post on the internet telling us you rock at cornering becuase you've got your foglights on.