Sanding Revisited..
I have the good fortune because of my job to know several top turners. Some fall more into the art turning or sculptural turning level, others are true production turners who work at piece work and can turn like demons. One common thread runs true for both, only turn as clean as is prudent to get the piece of the lathe as quickly as possible. In professional turning time is literally money.
While all of the turners turn cleanly, they all have a habit of stopping when too much cutting will not yield any better results, and get the sand paper out to finish their work.
If the piece is cleanly cut, you can start sanding with 120 grit or 150 grit, and usually stop at 220, unless they are making a high end art bowl or turning.
The general statement is you reach a point of diminishing return with tool work, and it is more prudent to get the sand paper out and finish out as quickly as possible.