The ECU has an adaptive strategy which is designed to compensate for mechanical variance and wear and tear. Basically the ECU will adjust a setting and use feedback from the sensors to see if it has made things better or worse. If it has made things better it will store the setting and use it from now on and so on.

This is just fine tuning, it is not the same as a remap and it Is not clever enough to adapt to a different engine etc. Every now and again it does not hurt to wipe the KAM as it could be hiding faults etc.