Zuckerberg says this helps culture at Facebook because employees are familiar with one another. "By the time that you build this management team of people who have been in the company," he says, "they've all been working together."
"They know how to get things done and there's good trust, and good alignment on values," he adds.
As a result, this leads to another benefit for new hires: hope for progression in the company.
"It sends the signal to everyone else in the company that they can be those people in a few years, if they do good work and really excel," Zuckerberg says. "I think that that's pretty powerful too."
Like this story? Like CNBC Make It on Facebook.
7 things you may not know about self-made billionaire Elon Musk
Why having friends at work will make you a better employee