Economise? It's no good! (7)
I believe the answer is:
useless
'no good' is the definition.
(I've seen this before)
'economise? it's' is the wordplay.
I cannot really see how this works, but
'it's' could be 'es' ('e' can mean 'electronic' which is similar to 'IT') and 'es' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for useless that I've seen before include "Unserviceable" , "Serving no practical purpose" , "Counterproductive" , "to no avail" , "Poor" .)