Although I have them, I don't see the benifits, even on country lanes.
In town, I believe they have street lights, so there is somthing wrong if you need a fog light on to help you see at a junction. Out in the sticks, speeds will generally be higher, so the cornering lights won't be activated when going around bends. You may think that they would be of benift when pulling out of junctions into an unlit road, but this is not the case either. Many country folk will turn down to side lights briefly to enable any light cast from headlights of other cars to be more visible.