Extra roles for useless people (5,5)
I believe the answer is:
spare parts
'useless people' is the definition.
Although both the answer and definition are plural nouns, I can't see how one could define the other.
'extra roles' is the wordplay.
'extra' becomes 'spare' (both can mean left over).
'roles' becomes 'parts' ('part' can be a synonym of 'role').
'spare'+'parts'='SPARE PARTS'
'for' is the link.
Can you help me to learn more?
(Other definitions for spare parts that I've seen before include "accessories" , "offered for replacements" , "Pare straps (anag.)" , "Replacement components" , "Don't be merciless on everything" .)