The key left for a guest says arrival is expected even when nobody can be there.

A key put out in advance does the work of a welcome with nobody present to give it. It says the visit was thought about, that the arrival is not an interruption, and that the guest is trusted with the house. Absence at the door can feel like indifference; preparation corrects that before it happens. Hospitality is largely arrangements made ahead of time.

If you cannot be there when somebody arrives, leave more than the key. A note with the wifi, where the light switch is, something to eat. Ten minutes of thought spares them an hour of hesitating.