For example, 'take + SBJ + OBJ:part + in' is proper, while 'take + SBJ + OBJ:part' is not proper (because not complete), and 'read + SBJ + OBJ' is proper, while 'read + SBJ + OBJ:book' is not proper (because not clean).
free slots in pVCCs are complements (subject included) and fillers in pVCCs are idiomatic, carrying some special meaning.