You need a form of engagement document, but you don't necessarily need customised letters. An engagement brochure meets the requirements of APES 220 Taxation Services and APES 305 Terms of Engagement. You should make sure the client acknowledges receipt.
Engagement letters are important because they outline the expectations and responsibilities of both the bookkeeper and the client. They also help protect both parties in case of any disputes or misunderstandings, especially involving the scope of work to be completed.
An engagement letter protects the firm by provide a record of the contract between your firm and the client, and minimises the risk of any future misunderstandings between the parties. Information on the best ways to develop relationships with your clients.