Here is how it works. All you need to do is find your item, and then scan the bar code with your mobile phone. The application handles the purchase, and so you can walk into a store, scan, and walk out with the item. If someone at the front gives you any guff, just show the receipt on your smartphone.
The application can also do QR codes and NFC tags, and the application can do gift cards, debit cards, and other types of store credit.
I suppose that we will soon see an age of just taking stuff off the shelf, provided you pay on your smartphone. That means there are no more check-out lines, but I see an age of a line at the door to check receipts. This already happens at Costco, along with the check-out line.