few things are more inefficient than the time between finishing a meal and paying the bill.

if you could check in to a restaurant and open a tab with your wallet, you could pay and leave whenever you want.

when an order is placed, the funds move to escrow.

if you walk out and forget to close, a smart contract executes a transfer to the restaurant's address after a reasonable amount of time.

if you send something back to the kitchen, the restaurant can set a split for the item to refund from the escrow balance.