Hi Dave,
Really good question. I do not think we have an official list available, in part this is because many of the checks and fixes are practically impossible to explain in layman's terms. In a past life I was a Revit developer and I would have a really hard time understanding, let alone explaining, some of them. Usually audit checks clean up minor inconsistencies like incompletely deleted objects, incorrect element relationships, or bad data. Typically they are the result of bugs that we have fixed in the software and audit ensures that the file no longer contains remnants of those bugs. In some rare cases, we do not know the origin of the issue, but we can easily fix it. Any output generated by the Audit process it output to the journal, but not all checks are required to do so.
One recent example of a check added to Audit is the 2015 family corruption problem. While audit cannot repair the corrupt families (due to missing information in the file), it does clean up the family so that it does not cause crashes and can be easily replaced by reloading the family from RFA. Any families identified as corrupt by Audit are written to the journal.
In general, because issues resolved by Audit are the result of bugs, there's not a lot end users can do in terms avoiding them, however what you can do is to make sure to upgrade to the latest service packs when they come out because the issues may very well be solved on our end. I wrote an article about this a few years back. It really is worth your time to update to the latest bug fix releases.
Thanks,
Sasha