Think of archiving a user as moving them to a 'Do not contact further' list.
Sample use cases for archiving users in the review manager:
If you accidentally upload a client you don't want to reach out to with a review campaign-->move to archive
If a client is in an active campaign but you want to stop the campaign-->move them to archive
If a client has finished a campaign and you don't want anyone on the team to 'followup' or reach out again-->move them to archive