The Little Guy!
One element of the studio system that is often overlooked is how it provided stable work for just about everyone, including the supporting cast and many of the extras. They didn't make the same amount as the bigger stars, but they were able to establish their families and receive full benefits as employees of the studio.
They had less control over the roles they took than the big names did, but then most of them were just happy to have steady work. An additional benefit of doing what they were told was that it could lead to bigger roles and larger contracts. They were also guaranteed a ton of screen time because the studio had to pay them regardless of how much work they did, so it behooved the studio to keep them working.
So why would a big studio like MGM want to keep such a large group of second tier stars under contract? The studio's constant need for content meant that Louis B. Mayer needed to keep the cameras rolling. Having a standing army of talent at his disposal meant that he could instantly summon an actor or actress to any production. His crews wouldn't have to stand idle for too long waiting for production to resume. Thus he could keep his well oiled machine humming along.
Today, most actors and actresses have to hustle for work. They get paid per project and have to make their pay stretch to last throughout a dry spell. The studio system might not have been perfect, but there were more than a few people who might have preferred it to what came later.
