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
Used to say that an action, even a pointless one, will do no harm either, so it might as well be done. Pronounced "sé fa pa dé bin fa pa dé maou", it gives the green light to a harmless gesture, as in: "Shall I wash the plates while taking them out of the cupboard? Well, se fa pas de bèn, fa pas de mau!"