[Dean]

While it is not set in stone, the Impreza chassis typically like about 1 degree less camber in the rear than the front for optimal handling. Of course this entirely depends on the rest of your suspension and driving style, but it is a fair guideline.

It also gives them a more even wear pattern if properly rotated.

Remember, the typical way to setup a car is to set the front for optimal traction and adjust the rear for feel. In the Impreza, this often means standing up the rear tires (less negative camber, AKA closer to zero) and stiffening the sway bar to give the rear a little less traction so the car feels more neutral.

The problem with standing up the rears is they may rub, especially on a wagon.

Again, I could spend hours talking about setup, but that is not bad for a couple paragraphs.