For me, it's about doing the most with the time I have. Hiring a freelancer can help businesses complete what they need to in a shorter period because there are more hands on deck, so to say. This means they are able to do much more, which factors into their revenues and profitability.
Also, good freelancers let business owners focus on running the business and getting clients through the door, two things that led to the success of everyone involved, even the freelancers.