While fog lights are beneficial in fog or any other glare-producing conditions, they can also help you see better when you drive on a clear night. Mainly when you think of fog lights, you think of fog. You see in foggy weather by lighting up the road under the fog, illuminating as little of the fog as possible to avoid producing glare. Fog is defined as a thick cloud of water droplets, 0.00039 to 0.00156 inches in diameter, suspended in the atmosphere at or near the earth's surface and reducing visibility to below half a mile. You're being blinded by the glare of your own lights reflected off the water vapor in front of you.
Similar experiences occur in rain, snow, dust, etc.
The amount of glare from the airborne moisture is affected by the relationship of angles between your line of sight and the angle of your car's lights. That's why you want a wide, flat beam from your fog lights. What you want your fog lamp to do is light up the road in front of you without lighting up the fog that's higher up, right in front of your eyes. The cuts in the lens, called fluting, shape the pattern by how they deflect the light. That's what it would be if it had a totally clear lens, with no fluting.