are just giant shims for your front upper control arms.
The rear will usually stay in spec even with the lower springs. If you get adjustable upper control arms instead of the 300 Degree kit, you'll spend a lot more money and you will have to also buy adjustable tension rods. Your alignments will get a lot more *interesting* with all those adjustable links, too. Get the 300 Degree kit unless you need all that adjustability for racing or sumthin'.