The client is hiring you because you have some expertise that they do not have. What you don't want is for the client to use you to develop their own expertise and then not compensate you for the information that they're taking from you. Similarly, you most likely will view some of your client's confidential information in the course of providing services for that client. Your client and you may bind yourselves in the Services Agreement to keep each other's confidential information secret.
Sometimes, you or your client will prefer to keep the existence of your business relationship secret. To avoid misunderstandings, the Services Agreement should include provisions that detail whether the parties may publicize their business relationship and how that publicity may take place.