Basically, it's a way for the device to shut off instead of shorting out if there were to be a surge in current. Batteries sometimes are protected, but if you use a device that isn't protected it could end up shorting out your battery or the device you're using for the jump. That's where the short circuit comes in, it basically returns current in a safe manner to where it came from, diffusing the situation before it damages anything. There is a lot of information on batteries out there, but here's a good lesson on safeguards that are in place for batteries.
1 - http://batteryuniversity.com/learn/article/safety_circuits_for_modern_batteries