Impractical advice for someone trying to economise (7)
I believe the answer is:
useless
'impractical' is the definition.
(thesaurus)
I can't explain the rest of the clue.
(Other definitions for useless that I've seen before include "Of no practical or worthwhile application" , "idle" , "Of no practical application, not worth keeping" , "Poor" , "Is Sue less impractical?" .)