Not sure about freelance, but for a salary in my experience, answer some recruiter spam on LinkedIn. I always thought they'd be crap since they are spammy... But after using some I've totally changed my mind. At least in my industry (silicon verification):

• Companies use them.
• You get a foot in the door & can bypass all the HR crap.
• They know all of the relevant companies. I learnt about my current company from the recruiter.
• They give you some hints about the interview process.
• They do all of the chasing up for you.

Also, they get a big payoff if you get a job, so their interests are more or less aligned with yours. The only slight difference is that they just want you to get any job, so they might push you to a job you don't really want. But it's minor.

Basically you get a lot of benefits for using them and you aren't paying the cost - the company is. They won't pay that cost to you if you don't use a recruiter and save them cash, so there's no real reason not to use a recruiter.

It may be very different for less niche sectors; I don't know.