they throw the geometry off. the x2 ball joint from steeda can help put things right. the tie rods and the lower arms need to be in line with eachother. ideally, the lower arms should be parallel to the ground and in line with eachother.
when people slam the car on the ground, often times the control arms end up pointing at the sky. this puts the front roll center height below the surface of the pavement. (not a good thing)
but people like the slammed look so they keep selling the springs...