One of the biggest benefits from acceptance testing for me was that the teams finally get a source of information on what goes on in the system as reliable as the code itself. Without acceptance tests, code is the only thing you can really trust and any other documentation gets outdated very quickly. Acceptance tests stay relevant throughout the project because they are automated, and automated tests are kept up to date in order for them to pass. Automation, and consequently a tool, are necessary to get this benefit.