Literal translation
if it does no good, it does no harm
Meaning
it does no harm and no good, so why not do it
Explanation
This expression means that one may do or attempt something without risk, even if the outcome turns out to be pointless. It rests on a balanced double negative: the action considered may bring no real benefit, but it will cause no harm either, which is enough to justify doing it out of plain common-sense caution. The word mau, covering pain, evil, and harm at once, anchors the phrase in concrete vocabulary. The register is familiar and slips naturally into everyday conversation, for instance to justify some small domestic gesture of little consequence, or to encourage someone to try a step that carries no unfortunate risk if it fails. The example given in use, about washing plates while taking them out of the cupboard, shows the very ordinary register of this phrase, in its wholly practical register: it mainly serves to defuse needless hesitation before a harmless gesture. It sits alongside the popular common sense that favours measured action.