waste of effort
waste of energy

Any further effort to do so would be a waste of time and energy.

Everything else seems like a waste of time and energy.

His father considered talking a waste of energy, he said.

It is a waste of life and energy, nothing more.

You told me it was a waste of my time and energy.

At any rate, it seems to me a waste of energy to try to learn what is beyond my understanding.

It was a waste of energy, but they didn't know that yet.

Until then, it was a waste of mental energy to try to second guess what would happen.

Ah, can you not see that it is a waste of time and energy?

Proving who did it would be difficult and a waste of energy.