Wasn’t Olivia Hussey barred from attending the British premiere of Romeo and Juliet because of the rating it got due her own nudity?
Mostly I’m the accountant, but I do get to go on set sometimes to see what’s going on. My wife has a film degree, and is occasionally a producer. We’re minor players, certainly, but you could find us on IMDB.
They are mostly smaller projects, such as one shot primarily on a green screen set that a guy built in his garage.
I did overstate things by phrasing it as if it’s always done the way I described, but I find that most questions like the OP’s stem from thinking that movies are filmed the way they happen.