Sounds like an easy way to cheat retail stores. What is the purpose of this technique? Lost your ticket, but remember the barcode? I've had the ticket office print me off a new ticket since I'm a STH.
It's no different than the "your card is your ticket" nonsense the Nats are doing next year (or what airlines do now). The bar code is deactivated the second it gets scanned at the turnstile so I'm not really sure how anyone is "cheat[ing] retail stores".