Front fog lights should only be used in cases of extremely poor visibility caused by dense fog or falling snow. They illuminate only a few feet in front, and provide illumination of the kerb, when you would otherwise not be able to see the few feet or so to it. They provide no useful illumination beyond this.
If conditions are such that you can drive faster than about 15 mph, then you are unlikely to get any benefit from using front foglights.
In better conditions, front fog lights have the disadvantage of brightly illuminating your close field of vision. Because your eyes react to this bright light they lose their dark adaptation, worsening your distance vision.
In wet conditions, their shallow beam angle can reflect off a wet road and dazzle drivers approaching from the opposite direction. If poorly aimed, they can dazzle just like a badly aimed headlight.
Fog lights are frequently used as 'driving' lights, and as more cars start being fitted with front fog lights this problem is worsening. In particular I've noticed a growing trend of people driving only using side lights and fog lights for illumination.
The simple solution would be for manufacturers to add an interlock to the front fog lights, such that they can only be switched on when the rear fog lights are switched on. Rear fog lights are needed in moderate fog, and conditions of heavy spray. I cannot think of a condition where you would need front fog lights and not the rear lights.
One manufacturer, who shall remain nameless, obviously thought they were on the right track, but got the interlock the wrong way round. On their cars, you can only switch on the rear fog lights if the front fog lights are on. Doh!