Saying for not doing something because it is futile [duplicate]

Question

Is there such a saying? Futile may be either because it will fail or because it is unnecessary / already taken care of. I considered:
too many chefs spoil the broth

and

It's like carrying coals to newcastle

But neither are very good... A formal sounding colloquilism is also ok.

Answer 1

You could use

beating a dead horse

Or

carrying water to sea

But why not just use "pointless?"

Answer 2

WOMAT (waste of money and time) may do to express that.