SMS_DEF.MOF vs. Configuration.Mof
SMS_Def.mof is used by Configuration Manager to create the Hardware Inventory Policy. It is where you as an administrator would change TRUE to FALSE or FALSE to TRUE to enable to disable existing classes and attributes, or if you are adding custom classes, where you would paste the customizations to the bottom of the file. Configuration.mof is where you would paste customizations to the bottom of the file. Changes made to configuration.mof are picked up by the clients and automatically compiled. It where a client finds out “how” to report on custom hardware inventory requests.
A detailed explanation may be found ––>Here<––