why use the wedge that comes with the shackels?

 

When you alter a vehicle height using things like shackles, different springs etc, you effectively alter the pinion angle. Change the angle you affect things like U-Joints, transmission tailshaft seals, differential seals etc. You add alot of vibration, harmonics etc up to and including driveline failure and that's a safety issue.

There are better solutions than using altered shackles.