Presentation: A recruiter introducing you to a client company makes you stand out from the crowd. You're put forward by a trusted source.
Security: A company paying for a search is generally financially strong and is more committed to your success.
Hidden job leads: Many searches are confidential.
Preparation: A recruiter's income depends on you landing the job. They can give you insight into the hiring company and interviewers and help you present your skills and abilities effectively and favorably.
Negotiation: We do this all day, every day. In the same way that a lawyer who represents himself has a fool for a client many job seeking professionals are best represented by trained and experienced advocates.
Buffering: A recruiter serves as a useful information channel between you and the company.