Imo
For me it depends on the amount needed to take off. Currently I'm only turning for my .330 neck Ronnie Long 30BR. I turn those in one pass (using a drill and a case holder).
For me, I take 1 turner, set the mandrel and cutter where they need to be, and tighten them down nice and snug, and then never touch it. If I get another gun with a different neck diameter or different neck thickness, I buy a 2nd turner. It just gives me a good feeling that I did not "change the setting" and it makes me more confident in my turning process.
MY DEFINITION OF ONE PASS: I set the turner at the desired thickness, and I turn the neck nice and slow as you described. After wipe down, and relubing the case neck again (without moving the setting on the cutter) I turn it again with a faster brass spinning speed, and a slower movement of the cutter down the neck almost to give it that polished or smoother feel. I find my necks all turn within +/- .0002 in thickness.