I can perform a Purge on one or more contexts in Windchill. The object query for each purge specifies to search for both WTParts an EPMDocuments (CAD models). When a purge is searching for WTParts only or EPMDocuments only, the purge will be far less effective because of the association between the WTParts and the EPMDocuments. Only a purge on both types together seems to work (in most cases).
For drawings, this is much easier. Drawings have no active association to WTParts and it is easy to use the Delete Non-latest Iteration. Fairly large drawing with a significant number of iterations can be purged individually and make up for quite some disk space in the vault.
That particular scenario doesn't work on assemblies however. When asking to remove the non-latest iteration on an assembly, Windchill states this is not possible due to the association with the WTPart. I also want to delete the non-latest iteration of that part (if possible), but I have no preference to also perform the operation on the associated part. As an alternative, their could have been a collector so the associated objects could be collected before the purge starts.