The Save SDC from Assembly command enables you to select an Assembly in Revit and save the Smart Assemblies Configuration to your computer.
The command is useful if you need to retrieve a configuration from a previously-created Assembly, if you want to save a configuration for an assembly with an Instance Configuration (see SDC Modify by Instance help file), or if you received a file from another person.
After selecting Save SDC from Assembly command, you will be asked to either change the name of the new configuration or tick checkbox to Overwrite Existing option.
You will also have to do the same with Dimensioning Rules.
After you save it, you will be able to use this configuration on other assemblies.
Note: Configurations of Smart Dimensions will not be retrieved with this command.
Also, it will work only if Assembly was created with configuration, which has this option ticked ON: