Why is he being told to reset his ECU? Problems?

The ecu is reset whenever the battery is disconnected... so if you loose power everytime you change the battery, that's a pretty lame setup. As far as I know resetting the ECU won't hurt anything. ECU is just a computer... does turning your computer off at night make it slower the next day? Not mine.

From what I understand, OBD-II will "learn" what mods you have and adjust for them to be basically eliminated. Resetting the ECU will make it forget and get that power back. Untill it relearns which is a couple hundred miles.