Well, I'm obviously not arguing you should hire indiscriminately. I just think that asking "will the employee be essential to the existence of the company?" is

Well, I'm obviously not arguing you should hire indiscriminately. I just think that asking "will the employee be essential to the existence of the company?" is the wrong test for deciding whether to hire someone. Employees are toxic. That is over-simplified to the point of being almost content-free. Beyond a certain point, adding more engineers to a team obviously decreases total productivity (per MMM); that's not to say that there's no value in, say, adding new sales engineers to support new customer engagements, or adding new employees to kick-start an entirely new project.