I never left the States?

What happens if the green Departure Record is still in your passport when you return home from the US? Well then you have never been registered as leaving the country! This may not sound as a problem to you, but since the normal visa allows visitors to stay for a maximum of three months, not registering your leave means that after three months you have exceeded the maximum stay, and may face serious trouble next time you want to apply for a US visa!

The good news is, that if you did not need a special visa in the first place, e.g. if you are from EU, and you left by scheduled flight, your passport number was registered with your boarding pass, so it is easy to show that you did indeed leave the US before the end of the three months.

Read more at the US Customs Border Protection