The person laying an extra place has made generosity visible before the guest arrives.

Setting a place for someone who has not arrived is a statement made in advance. It says the welcome was decided before the person had to ask, and it removes the awkwardness from arriving. Hospitality is often imagined as what you do once people are in the room, but most of its warmth is arranged beforehand, when nobody is watching. Preparation is a kind of message.

If someone might come by this week, make the small preparation that says you expected them. An extra chair, a spare key, food enough for one more. It costs little and settles the question of whether they are an imposition.