Too bad all smiths didn't have equipment that "tight". They could dial it in at a fraction of a tenth and then use they could use all their old reamers because the pilots wouldn't even touch! Biggest advantage of using no pilot would be to a more effective flushing during operations. The setup for quality chambering is most important. If the lathe won't hold the tolerance, no amount of setup and prebore is going to make the chamber "true". The benefit of more effective flush is probably the biggest advantage, similar to cutting a chamber by hand with frequent cleanings every .010 or .020.
The end result of a "clean", "round", concentric to bore is attainable in more than one way.
The term "precision" is being used pretty loose and actually would be an insult to a bunch of top end smiths who build rifled for a host of competitors and "national champions".