We are only referring to the rubber isolator between the spring and body in the rear. You DO want them. Otherwise they will conduct all the noise and NVH directly to the body. Racetep offers 2 heights, stock, and +1/2". Your car should already have the stock rubber ones. So, unless they are broken/rotten, no need to replace em.
That being said, i have the + 1/2" ones, i like em.