When you're driving inductive load (relay solenoid, motor, etc..) you need to put a 'flywheel' diode across the output of your driver circuit to make sure that none of the induced electricity when your driver TURNS OFF but motor continues turning (on it's own inertia) can damage any of your sensitive components.
The flywheel diodes inside ULN2003 are all connected together to one common port (pin 9 or 16 if I remember well) and they carry the load of any inverse current that gets sent across by the inductive part.