Haven’t watched his videos in a while, but:
1) he probably gets discs for free
2) he insists on using every grit, like from 80-100-120-150-180, etc
1) He might. As employees, we all did too. No one was deliberately wasteful, but time is money too. If going through paper faster, made the job faster, all good.
It's not wide-open-silly, there are some guiderails in place, but management always said, "If you need something just let someone know." There are a couple of people who are designated for such things.
2)With plastics, you really have to, unless you intend to stay at a specific level of dullness. Solid Surface is almost always done like that. It's rare to go to full gloss. It can be done, but it is not recommended, at least by me. It will take that level of polishing, but "in use" (especially in public) it will not stay that way. Just the fingers of a grown man, who works a manual job, will scratch it. Corain (and the like) will always "wear" to an equilibrium. If you leave it to dull, normal use will polish it. If you over gloss it, a natural dulling will take place. The only hedge against it is customer/client maintenance.
Lighter colors make it less noticeable.