Don’t think you can use the out of box workflow (document approval) as an audit trail on a long term basis by default. Workflow history is deleted after 60 days. (And don’t just deactivate that feature in Central Admin, the log files will get too big and ten other things will fall over). So for example, if you are using workflow to approve board meeting minutes, the approval status you see in the document library now will not display in 60 days. Your auditors will have an issue with that. You need to speak to your techies for workable solution if you are planning on using SharePoint as an audit source.