Well.....they adjust your caster and pinion angles. You should be concerned about caster angle in the front, which is the angle between a straight line between the king pins and the level road, this is usually tilted with the top slightly behind the bottom king pin giving the wheel "trail." That is, the contact point of the tire is behind or trailing the intercept point of that straight line between the kingpins and the road....this is what causes the wheel to "self center" so to speak and be stable - look it up on google for fancy pictures, etc.
In the rear, the pinion angle is the relative angle of the pinion/yoke and the joint on the rear of the transfer case. Depending upon lift and joint type (Rzeppa or CV) the best pinion angle will vary. With a lift of up to about 3 inches on a 2dr, not much to worry about with stock Rzeppa joints - but over that much lift, one has to be more concerned as the joint angle becomes excessive and can tear or rip the rubber boot. Search is your friend on this...many good posts that go into detail. Just 2.5 cents in this case.
08 JK 23S - Colorado Jeep Club No. 204
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16 JK Rubi with all the trimmings
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