Lee did the same polishing on my valves. He is not using an abrasive like a lapping compound, just something akin to the Flitz that I use. There can be deposits that build up over time and are the very dickens to clean off! Even my little ultrasonic cleaner won't get rid of such deposits, probably because to clean those I would have to use a fluid in the ultrasonic's tub that could harm the brass caucades in the pistons.
A typical cleaning at a shop won't get at the tough stuff. It is good for cleaning out the passages, so it is not money wasted. The Spitballs only help a bit, but at some point one has to get serious about cleaning the passages. Then the entire valve casing has to be cleaned separately, because the flush from a shop won't really touch that. Be sure to use a wooden or plastic tool to scrape out the slot that the valve guide travels in. Then clean bottom and top caps.
Even with all that, it can be very hard to get all the little curvy passages clean, especially the short runs between valves. That's were the shop's flush might do the most good, assuming the allow ample time for the build-up to soften and flush out.