We replace 3 or 4 a week, mostly on the M112 engined late 90's cars. The scanner they are talking about reteaching rotor adaptation (along with clearing the DTC if the CPS triggered a code). Rotor adaptation should be reset whenever CPS's are changed or engine mounts are changed - it deals with incongruencies in timing due to torquing of the motor (you change relative timing just by putting a lever in the engine compartment and prying over on the engine while its running) or other effects and hiccups in timing.