In Bangkok they issue boarding passes as long as the next flight out of HKG is 24 hours or less than when you arrive in HKG. I arrive in HKG at 7 p.m. with BP and lounge invite and the works for a next day flight out at 4:45 p.m. so for an overnight sleep stop it is quite handy.

Can't see it being much use at Airport Express unless you have a bag to lug around and it is close enough to whip over to get rid of it. But then you use your fare for the train to enter the station to do that.