It puts the vehicle into a place where you can set the base timing and idle speed to what it should be.
One thing to note is that it should be at operating temperature (coolant temp at midway is a safe call).
Just to confuse matters you should hear the rpm decrease as you bridge out the terminals. If it increases the ECU may be seeing an incorrect signal from the throttle position sender. In this case you could find the timing mark isn't even close to where it should be. Usually it's just a case of adjusting the TPS sensor back to within tolerance to sort matters.
Jay