To what extent does Smriti injunctions regarding worldly motives (Hetudardhana) apply?

From what I know, Smriti injunctions that have worldly motives are not authoritative. The word for worldly motive is actually “hetudarshanam” or “view to a reason”. I imagine this is a perceptible reason or a deducible reason? How true is this and to what extent does this apply?