Hi Rick,
As you may know, with D365 you can have multiple Business Process Flows (BPF) associated with 1 record - for e.g. an opportunity may have a marketing nurture BPF as well as a Sales BPF running. The idea behind the Finish button is to mark which of the Business processes have been completed.
Note: Once, you click 'Finish' you cannot move to other stages using the UI for that BPF.
When you click the 'Switch Process' button for that record, you will now see this 'Finished' BPF on the Archived list - since it is no longer active.
To the second half - no you cannot add the field to the view using the user interface but you can query against it using Advanced Find. The query would go something like this:
Entity: Opportunities
--(under Related Entities) - "Opportunity Sales Process (Related Opportunity)": "Status Reason equals Finished"
Hope that helps,
Regards,
Shubhangini
