[māu] (rawa) ka aha?
1. what will [you] achieve by that?, what difference will [you] make?, what can you do? - an idiom suggesting that there is no point in doing something.
E mea ana au me peka atu ki tō rāua. Māu rawa ka aha? / I am saying that we should stop off at their place. What is the point of that?
See also mā tēnā ka aha?