Open a desired assembly that must be reduced to shrink file or protect intellectual property
Menu Bar→Tools→Defeature
Select a simplification method
Each type will reduce the group differently
It is most common to select external and interface components
LMB Add Group to process the selection
Repeat the process by adding new groups/simplification methods
There are limitations to how many components can be simplified per group based on hardware capabilities
The preview on the screen is a multi-body part model
LMB The Right-Arrow then Save the defeature as a new part document
By this point, it's unlikely there are additional bodies that are to be removed, but bodies that are "accidentally" removed would be added to exceptions list
LMB the right-arrow
Add any holes (interface holes especially) that are to NOT be removed
LMB the right-arrow again
Go back to the previous screens to add exceptions as needed
Save the Defeatured Part