This I found in a Quora forum on prepaid meals in China:
The difference is that customers who haven’t paid can justify their occupation of a table. They surf facebook. They chat away for hours on end. They get comfy. It matters not whether they intend to order more stuff, the mere possibility of them ordering more gives them the moral upper hand.
Customers who have paid up on the other hand, do not have moral justification. They could order more food, but diminishing marginal utility and inertia discourages that act. They get edgy. They feel guilty. They leave.
It all depends on the restaurant’s business model. If it’s a low-end restaurant, this tactic will serve it well. If it’s a high end restaurant, paying $150 for that bottle of wine buys you a little more time.
For the pointer I thank Eduardo Pegurier.