At best I can see people thinking that is a easy to fool people into taking it easy during the break in process. Even then, break in process is equally debatable.
The other thought is it's perpetuated by some dealers to get you to come back to them for service instead of doing it yourself or at an independent shop, and I have heard some claims from owners that make me this claim is more likely. They say their dealers tells them that only they can install them plug during that service, total bs.
My dealer installed mine before I left with the bike on day 1 and they don't understand those claims either.