Reduce consumption? That's futile (7)
I believe the answer is:
useless
'futile' is the definition.
(similar in meaning)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for useless that I've seen before include "Unemployable" , "Far from impressive" , "Without purpose" , "Serving no practical purpose" , "Ineffectual" .)