Surely you still have 'check your baggage in' for weight purposes. The carrier may need to charge excess baggage where necessary.
Whilst you can check in online with most carriers, some still require visa checks prior to departure, depending on the passenger and the country they're going to. Australia springs to mind as a friend of mine who was told he had an electronic visa in his passport, on checking in found he didn't have one. The travel agent had cocked up and he was charged extra by the carrier prior to departure.