Sometimes a named object is rhetorically stronger than ellipsis, particularly when the listener is considering a wrong candidate and the sentence is meant to correct that supposition. Omitting the object could leave the misunderstanding in place.
If someone reports “He punished” and the important question is “Whom?”, the identification of the person affected supplies the missing information. This is a teaching illustration; the general principle is that an intended contrast about the object requires the object to be made clear.
Thus the principle of deletion has limits: an object evident from context may be deleted, while an object under dispute may need to be stated.