Dennis
Like you, I don't know why a primed case is necessary to fine tune a bolt & firing pin, unless it's the cushioning effect. But that would only be good for one time.
Cartridge collectors need to inert primers because we mail primed cases both domestically and International (except Canada). Many of us have tested the different methods, including a soak in #9, or any good penetrating oil. But, even though it seems foolproof, there are always a certain percentage of primers that will still light. Most of us put a note in the package indicating that the primers were inerted by soaking in oil and that seems to be good enough for Postal and Customs authorities (except Canada). But most of them are ignorant when it comes to cartridges so they take our word for it.
Military primers, being crimped in, can only be inerted while still in the case.
Ray