These recruiters act as matchmakers. The basic idea is that you don't know about all the companies that might want to hire you, so you can't send them your cv.

These recruiters act as matchmakers. The basic idea is that you don't know about all the companies that might want to hire you, so you can't send them your cv. You talk to one (or a few) recruiters and they do the leg work to talk to lots of companies to find the few that you would be interested in. If you accept an offer, the recruiter gets a substantial payout from the company that hired you. If the recruiter is good they save time for both the candidate and the hiring company. If the recruiter is bad they waste you time by trying to get you to talk to lots of companies when randomly sending out your cv would have worked just as well.