Benefit from merger, say, releasing a bit of work in city (7)
I believe the answer is:
synergy
'benefit from merger' is the definition.
(two businesses merging might have synergy)
'say releasing a bit of work in city' is the wordplay.
'releasing' suggests deleting specific letters.
'bit of work' becomes 'erg' (unit of work in physics).
'in' means one lot of letters goes inside another.
'city' becomes 'ny' (I've seen this in other clues).
'say' with 'a' removed is 'sy'.
'erg' placed into 'ny' is 'nergy'.
'sy'+'nergy'='SYNERGY'
(Other definitions for synergy that I've seen before include "Productive cooperation" , "Combined action" , "Beneficial interaction" , "Cooperative interaction" , "Coordinated action" .)