I have a post about some of these things in my blog
The AOW processed tracks Workflows that have “Repeated Runs” unchecked, so they need to track which records it was run on, to prevent from running again on the same record.
so you have to be careful when deleting rows form there. It’s likely that millions of rows can be deleted safely, BUT only you can know the meaning of your Workflows and whether it is a bad thing that they will be run again for some record.
So review the logic of your Workflows and then try to clean up stuff related to deleted records, for example, or cases where the “No Repeated runs” condition wasn’t really necessary.