The factory rear control arm has limited camber adjustment. When you lower you E36 or E46, street cars have too much negative camber and can't be adjusted out enough, and track cars can't get enough negative camber. These units will allow for much more camber to be added or taken away. Also, they are much stronger than the OE rear control arm so they can take the abuse of the uprated suspension typical of aftermarket products.

The IE race unit is an increadibly sturdy control arm with race bushings for the best precision possible. These are certainly streetable but were designed for hard track use.