For one thing, it causes positive camber in the rear if the SLS raises it enough to match the front. That is sort of undesirable in that it can cause you to go sailing off a mountain road in a turn and die in what is essentially a plane crash. Sort of like running around on the outside edges of your feet.

Plus it looks like schit, IMO. I'd love to lower the car an inch from stock so it does not look like something that belongs in a farmer's field.