M499 - EEPROM Invalidate Command

[Roxy]

So to understand the EEPROM default functioning better, what it does normally is give priority to the EEPROM ?

Your question does not make sense. But if this code is added to the firmware and used, it will invalidate the EEPROM contents. When Marlin initializes, it will use the default values defined in the Configuration.h file instead of using the stored values in the EEPROM.