This is not a question, but I am looking for a way to make travellers aware of this marvelous facility.
At Hong Kong Central and Kowloon MTR stations there is a dedicated airline check in facility for most major airlines. Hence it is possible to check in luggage and obtain a boarding pass up to 24 hours before your outward flight ( some airlines are limited to same-day flights.
Thus, divested of cumbersome luggage, one can shop, sight-see or have a relaxed meal without being confined to a sterile airport.
The fast and comfortable Airport Express train from either station then whisks you to your flight without having to spend boring hours for early check in.
More cities should provide such a service.