This is Whiteline's Anit Lift Kit or ALK for the GD chassis Impreza. What this kit does is change the Anti geometry of the car. It acomplishses this by slightly relocating the position of the control arm. From the factory, Subaru desings in Anti geometry. What this does is limit lift/dive characteristics of the car as weight is transferring front/rear. While this sounds good in theory, it doesn't allow for the suspension to as effectively transfer weight toward either end during a braking or acceleration event. Removing this geometry allows for better traction during these weight transitions.
Additional benefits of the ALK are that it gives the control arm a stiffer mounting point via a urethane bushing, which reduces the amount of dynamic alignment changes you get. (No unexpected alignment chages). It also increases caster which benefits these cars ability to suffer less camber loss during tight cornering. All in all, a VERY effective modification. This is the sport version, with a bushing duromter between the race and comfort versions, and the most commonly chosen by enhtusiasts.