I don't have any experience of working in film, so all I can do is try to understand this through my own frame of reference. In this case, that is mixing a piece of music. I know kleinbl00 has plenty of experience there too, so maybe he can confirm or deny my understanding. I'm far from a master mixing engineer, but what I've learnt over the last few years is that the mixdown process is greater than the sum or its parts. It hundreds of little changes that, in isolation, don't seem to make that much difference. For example, you could: - Add a compressor to make sure the volume of a vocal performance stays consistent - Add some subtle timed delay to a snare drum to give it a greater sense of power - Setup sidechain compression between the kick and the bass so that they're not fighting for space in the mix As a composer, it's very easy to look at those things and think: "none of that stuff is stuff I care about". I care about the arrangement, melodic themes, and chord progressions. They're the big, important things. What difference is a bit of EQ going to make? If the listener is focusing on the vocal compression then there's something more seriously wrong with the music. But if at the end of the mixdown process you reverse all those tiny adjustments, suddenly you're greeted with a significantly more confusing and harder to understand piece of music. Yes, a lot of the changes can seem almost subliminal and inconsequential to the average ear. But add enough of those subtleties up and suddenly it's not so subtle. And ignoring them all results in less comprehensible and immersive experience for the audience. That's why there's a professional their who can sense those things making those changes.
A better analogy is that of a tracking engineer to a mixing engineer. If the snare drum has a couple busted snares on it, no amount of plugins and Class A circuitry is going to make it sound good. The mixing engineer may have no idea how to dress a drum kit to get it on tape in a viable way. They may be an absolute genius at a Phil Spectre wall'o'sound but be incapable of getting a barbershop quartet in the can. The talented ones, however, know that their success relies on the success of others upstream of them. I have a really hard time making dialog sound good if the actor's sweater is rubbing on the lav head every time he raises his arms. As a post production sound mixer, "clothing noise" is either something I subtract through surgery and liberal application of plugins and trickery or something I add through foley. But as a location sound mixer, "clothing noise" is 50% of my job. When I've worked on stuff for WB or CBS or HBO or paramount, the scriptie sets up right next to me, with a video tap, recording every take and noting the position of everything that moves in the course of the action. They take shots of hair, makeup, wardrobe and set decoration for every single setup. When I've worked on stuff for Youtube there's no scriptie. A character running in the wides and walking in the closeups is the kind of boner that the extras will call out. I mean, anybody who has been through a little film school knows the 180 rule. Without a scriptie, it's possible that the 180 rule isn't going to be applied to inserts, especially as that's likely 2nd unit and they're out on the hunt without any direct congress with 1st unit. That's usually how stuff like this happens. Your greater point - a million little things that the audience doesn't notice add up to the difference between mediocrity and greatness - is apt. But it's more noteworthy to point out that editors are reliant on script supervisors to give them material to cut... and that they rarely meet. Post is rarely invited to wrap parties because they haven't even started working yet while everyone else is taillights.