When our flight made an emergency landing last year, they wouldn't let anyone leave the secure area because nobody had a BP that would let them back through security.

I bought a ticket on the next flight out just so I could leave, buy some food and come back. Worked fine then. Cancelled the ticket about an hour after I bought it by calling DL (wasn't even a refundable fare, but was obviously within 24hr). I'd say, just don't make a habit out of it ;-)