Yes, they for example provide access to clients not willing hassle to work with a single individual. If the candidate is leaving they may provide a different

Yes, they for example provide access to clients not willing hassle to work with a single individual. If the candidate is leaving they may provide a different one. And the client can negotiate several candidates at a fixed rate and the agency can provide different insurances and help with taxes an so on (for both parties). A good agency would also help with the negotiation towards the client. And find you a new client if the client drops you.