Not every deletion improves expression. If several mutually incompatible interpretations remain and no clue selects among them, the result is damaging ambiguity, not successful rhetorical concision.
It is one matter to show that some omitted content is conceivable, and another to establish which content is intended. Reason can sometimes establish the first; context, convention or habitual usage may be needed for the second.
The purpose is not simply to reduce wording, but to retain complete intelligibility with appropriately economical speech.