Below you will find body reinforcements. If you drive a form of motorsport, there is a very large load on the car body as it is not built to be driven in such a violent way. A body is built to be a bit flexible as otherwise after many kilometers it will crack in the welds etc. When you then drive eg, and rally you want the car to be as stiff as possible, so it does exactly what you want when you turn the steering wheel. The reinforcements you find below are also made because weak points have been found on eg BMW E30 / E36 / E46. Ie. that you know that when driving hard, the body will crack in certain places. You can avoid this by buying the reinforcements and welding them on the body.