[wilf leek]

Chopper.

A moot point. From a "pure" or empirical engineering standpoint, centering the rotors in the calipers would be the natural thing to do. Stops pistons one side or the other from over-travelling when the pads wear thin. Also, with gross misalignment, the rotors might actually catch somewhere on the caliper.
Lastly, the handbrake caliper arrangement wants to "see" a centralised rotor. Any drag on those handbrake (sorry, emergency brake) pads overheats them and they can detach themselves from their backings. Had that a couple of times before I learnt how to adjust them properly.

In practice, a few thou off is probably good enough. I got mine to within that kind of tolerance, and it did take some shimming.

PS edit - Chopper, I just now realised that you were talking about shimming the calipers - this is not how it works, it is shims between the rotors and the diff drive hubs that are used to centre up the rotors, the calipers just bolt straight on.

Then more shims between the rotors and the driveshaft mating surfaces (i.e. on the other side of the rotor) set the rear end camber.