Sometimes they are issued to cover time lapses.
For example, my license expires 5/6/11, but I procrastinate and go to the DMV today, 5/5/11. They issue me an interim license until the real one comes in the mail (since otherwise I'd be driving around with an expired license). They are usually good for 90 days or something like that.
_________________________
With the lights out, it's less dangerous.