Hotel checkout is noon. Flight is 7 PM. The airport has no storage lockers, and who wants to go right to the airport anyway? Some cities are unsafe for carrying bags in your car. Hence, the need for a baggage pickup/storage service.

I realize this exists in modest degree in some cities. The way I envision it is the UPS-type step van makes pickups at the major hotels at designated times. At the airport, they have a small booth near the car rentals or baggage area, you present your claimcheck and get your bags. For those on long layovers who want to go off-airport, check-in and check-out is done in the same place.