Atmosphere is what sells the third drink, the dessert and the digestif.
Guests rarely name it, but they feel it within a minute of walking in. In a restaurant, harsh lighting and a tired room make people eat and leave. A room that feels right makes them order dessert, then a coffee, then a digestif, and stay for the conversation.
In a bar, a great ambience is measured in the third drink and the ones after it. A great mood becomes a great memory, and a great memory is the reason people come back and bring their friends. That return visit is what keeps a venue alive.