Originally Posted by Axey
Once the program is up and running, the receipt it spits out will be collected at boarding time and attached to your outgoing BP (like the current I94 stubs)
One of the positives of this system is that the traveller finally has a "proof" (receipt) that they left the country in the event they were challenged on a future entry. (That btw is also what my friend was told by the UA gate agent when he gave her the receipt.) I guess that won't be the case.