Certainly having a bow tuned by a knowledgeable bow tech is very important. Unfortunately, there are a ton of people working in the industry that have no idea how to properly tune a bow. You can tune one 95% to perfection without having the bow owner touch it. However having them there helps ensure that the last 5% gets done according to them and their mechanics. A person can have bad/wrong form, shoot an improperly tuned bow and yet they can still consistently hit the bullseye. How is that? Consistency is the answer. If you do the same thing 100% of the time, even if it is the wrong thing, then you will achieve consistent results that will then allow you to adjust your pins to the point of being a proficient archer. Never mind your form is shit and you bow is whopper-jawed.
Milo got my bow 95% right without me ever touching. What needed done was the peep installation and a draw mod swap, both things that cannot be done without me being there. The draw mod switch was done because I am used to a spongy back wall and the Strother Infinity has a rock solid back wall. After shooting it a few times, I need about an inch more draw and that is something Milo can't tell without me there to shoot it. Same for installing the peep. He can get it close (we are almost identical in draw length and anchor position) but he can't get it 100% right without me shooting it. So yes, it is important to be a part of the tuning process, but not 100% necessary. I would always recommend having your bow tuned by a true expert while you are present. But someone with Milo's knowledge and expertise can damn near fine tune a bow without you ever laying a hand on it.