An engagement letter is drafted by the company rendering the service, often with the help of a lawyer. It is than presented to the client, and both parties must sign in order for it to be legally binding.
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 set the terms of the agreement between two parties and include details such as the scope, fees, and responsibilities, among others. Some of the benefits of engagement letters are that they are legally binding documents, they reduce misunderstandings, and they set clear expectations.
Whilst professional bodies typically advocate for an initial engagement letter, best practices suggest that these documents should undergo an annual review. This isn't just a bureaucratic recommendation but a strategy to ensure the relationship remains fresh and relevant.