Being an affiliate marketer is like being a freelance advertiser. A company will pay you to advertise their products, but you are only paid on commission. You are free to run campaigns however you see fit (within reason, within TOS), and are paid based on performance.
This is our preferred way to work. It means that we have creative control and can work on our own schedule, without the pressure of a supervisor micromanaging out strategy. We are rewarded based on results, which is a huge incentive to work hard for our vendors!