Originally Posted by Doppy
I'd keep it available as proof that you left when you were supposed to. Because sometime, for someone, that data is going to get messed up, then when they try to come back into the country or try to leave again, DHS is going to try to lock that person up claiming they overstayed their visa.
I do think the paper could be valuable for preventing future mix-ups, however I don't think a person in such a situation would be "locked up". More likely repatriated to his or her home country (and
possibly disallowed re-entry to the US for either 3 or 10 yrs). Granted this is not a pleasant turn of events either, but it is not quite as harsh as being thrown in jail.