The last client I was doing work for required a boarding pass (screenshots of a mobile BP were acceptable) attached to the expense report to get reimbursed for flights - because apparently a hotel receipt, a rental car receipt, meal receipts, or my presence on site for an entire week wasn't enough to prove I actually flew the flights I said I did. But those screenshots saved my arse a time or two when I didn't have cell service or the SW app malfunctioned at the gate and needed my BP to scan.