What is an audit trail?

In an automated process this is not overhead, it is what makes the process defensible. It records what was said to a customer, what a system decided, what a person approved and when. A well-built system usually produces a better trail than the manual process it replaced, because it records at the moment of the event instead of from memory a week later. What has to be captured, and for how long, is a design decision made before anything is connected.