To reduce consumption is no good (7)
I believe the answer is:
useless
'no good' is the definition.
(I've seen this before)
'to reduce consumption' is the wordplay.
I cannot quite understand how this works, but
'consumption' could be 'use' (synonyms) and 'use' is located in the answer.
The remaining letters 'less' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'is' is the link.
Can you help me to learn more?
(Other definitions for useless that I've seen before include "idle" , "Incompetent" , "Vain, impractical" , "Without purpose" , "Vain - unavailing" .)