dddd

Truth is, that neither method is perfect in terms of preserving any adjustment that you can achieve before final, full tightening.

I like my method (turning both cup and lockring into final tightness), because it's trial and error either way, since tightening the locknut with the cup stationary also affects adjustment, while my method puts less gouging force on the lockring's spanner hook notches.

After one preliminary tightening, I end up backing off on the tightness in most cases, to allow slightly rotating the cup with respect to the lockring, so as to then (second try) arrive at a final adjustment with the lockring and cup fully settled into a secured adjustment.

The more tries it takes, the better it is that the force needed to turn the lockring is as low as possible, to keep from raising sharp burrs, stripping a notch or damaging chrome, and I can even bias the final adjustment a little with a bit of variation to my final, net torque (both tools together).

That the cup is rotating while under considerable tension from the lockring should settle the cup in the bb shell threads more completely, even more so if the threads have dirt, paint or rust in them as is so often the case.

Also, the lockring spanner distort's the lockring's roundness, the higher the torque applied there.

Lastly, that the few lockring threads are not the ones turning on the cup threads is also good in that this reduces the chance of stripping them, something that will never happen to the greater depth of adjustable cup threads in the bb shell.

This adds up to quite a few reasons. I surprised myself here.