Imagine a simplified model of the world, where the population suddenly increases by 1000 individuals. Of these newcomers, perhaps 50 will become policemen to ensure safety, 30 will serve as doctors to maintain health, 25 will take on roles as teachers to educate the children among them, 20 will become hairdressers to uphold appearance, 5 will work in factories to produce additional cars, and 1 might become a mayor, among other roles (these numbers are, of course, entirely arbitrary).
The common characteristics among these professions is that they primarily cater to the needs of the new 1000 people, and thus, their numbers must roughly correspond with the population growth. If the new 1000 individuals were to vanish suddenly, the absence of these workers would likely have minimal impact on the rest of the world.
This contrasts with professions such as writers, researchers, engineers, movie actors, YouTubers, or international journalists. These roles generate added value that can be consumed by an unlimited number of individuals, regardless of population size. It is worth noting that this concept is not solely tied to the complexity of work; roles that collaborate closely with these professionals, such as makeup artists working with actors or lab technicians assisting researchers, also fall into this category.
In reality, classifying people into these two distinct categories is likely an oversimplification, and the lines between them may be blurred, with many shades of grey in between. Nevertheless, I am intrigued by the possibility of determining an approximation for the proportion of work or workers that must scale with population size. Do you know a name for a metric similar to this or any estimates of what it could be and how has it evolved over time?
The clearest such case historically is food production: what share of the population is dedicated to feeding the population, vs. literally everything else? https://ourworldindata.org/employment-in-agriculture shows that this has declined enormously over time, and I’d describe that as the defining feature of modern industrial civilisation.
(though I think that your question is somewhat ill-posed and ‘extra value’ is almost undefined, it’s still pointing to some interesting questions about the structure of the economy)