GMC fog lights are very useful to provide extra glow on the road. Remember that the average good road visibility on the road is more than a hundred yards. If it happens to be lower than that it is necessary to use fog lights both for front and for rear. It might have happened to you that when you drive on foggy road, you tend to slow down. With fog lights, you can see the road clearer and farther.
Front fog lights are usually attached at the front bumper about 10-24 inches from the ground. But proper attachment should be considered so as to minimize the amount of return glare into the driver's eyes and to minimize glare into oncoming eyes. These considerations are vital when installing these set of fog lights.
The rear fog lights on the other hand usually a single red light as bright as a brake light. This can only be used in visibility under 50 yards. Of course, they are called fog lights because rarely does your visibility drop to such a dangerous level in normal rain or snow like it can in fog.