This automation periodically re-checks the overall status of any campaign that isn't already locked or fully Sent, based on how its queued/sent messages are progressing: any send errors move it to Error; nothing sent yet keeps it Scheduled; some but not all recipients sent moves it to Outbox; everything sent moves it to Sent. This is what moves a campaign from the Outbox tab to the Sent tab on your Campaigns list once every message has gone out.