This is quite difficult to explain.
Let me write something that will make sense.
Just as a beginner - it's to do with the ECU monitoring by calculation the amount of torque the engine is producing. It the torque limits/maps are not changed then your gain in power will be temporary. I am sure you have heard before of stories where the 'ECU adapted back to stock'.
No one explains this because:
1) Not many understand it
2) It's real difficult to explain