A car is limited by what space it can only enclose. The bigger your car, the more spacious it is. The more stuff you can fit in, especially when you are on a long travel, with everything you need in it, the better. Still, you are limited by what space you are provided for. How else can you bring along your bike which you plan to use at one point in your travel by going mountain biking along the hills and rocky mountains? How else can you tag along your bike in your limited car space?
That is what the kuat racks are for. With it installed on top of your car you get to use the vertical space you have left. You may still be limited by the size of your car roofing yet it is enough to bring a couple of mountain bikes with you if you like. If you are not going to secure bikes, maybe skis. If not, maybe you can use it for other voluminous items like suitcases or large boxes. Just make sure you can secure them with a rope and none will drop off while you are driving to your destination. At any rate, you have additional space vertically.