Most small properties run the rooms in one system and the restaurant in another. The guest experiences that as being asked who they are three times in one evening, and the property experiences it as restaurant charges that never reach the room bill.
Vestibel anchors every bill to a Party — the people being billed, whatever the context. A stay is a party. A dinner table is a party. A spa booking is a party. Each has exactly one folio, and an outlet folio can be posted onto the master stay folio as a single aggregated line at checkout.
The practical effect is that a guest signs for a drink at the bar and it appears on their room bill, correctly taxed, without anyone re-keying it — and that the front desk can see, at checkout, every outlet bill still open against the room.