Hi Paul,
The ECU stores learned engine- and driversettings in volatile- or temporary memory. Sometimes this memory gets corrupted, caused by 'interference' in the signal like electromagnetic fields, equipment transaction time-out errors, spikes in voltage, affecting the electronic circuits.
Theoretically, pulling the ECU fuse @ engine bay should do the trick. However, many topics describe people not being successful doing so and some settings (and errors) are still preserved, versus pulling the batterycable. Although it's considered a 'Q&D' method, one is sure that power to ALL electronics, circuits and equipment is lost, resulting in facory defaults or a hard-reset.
My dealer for example, just pulls the ECU itself, that makes you wonder..