Part Mapping is enabled by default for Change Service and Design to Fabrication.
When you Enable Detailed Part Mapping, the list of parts that can be mapped expands from just inline parts to include elbows, transitions, and tees. You can also map to parts that have been added to the selected service.
For additional information, see Change the Service for Fabrication Parts in Revit, Convert Generic Parts to Fabrication Parts, and Map Inline Model Elements to Fabrication Parts.