yes that's what it does, keeps the preload on the pinion gear. Some guys use washers to keep the preload, they measure the crush washer that is removed and use the appropriate amount of washers and a sleeve to replace the crush sleeve. I've reused and seen the crush sleeve been reused with no ill effects. It's uncommon for a rear end to come apart if everything is bolted back in. What you are doing with the adjustments is you are keeping the rear end quiet. If you don't have the gears meshing properly the rear end will be noisy but it won't explode. The back lash is most important setting but that is easy to do and like I said the shims that are in the rear end will more than likely be good for any carrier you put in. The carriers are all the same, the rear end is machined and everyone is slightly different so the shims are picking up the differences in the rear ends.
