When scenery is an advantage (5)
I believe the answer is:
asset
'an advantage' is the definition.
(I've seen this before)
'when scenery' is the wordplay.
'when' becomes 'as' ().
'scenery' becomes 'set' (a stage set).
'as'+'set'='ASSET'
'is' acts as a link.
(Other definitions for asset that I've seen before include "A useful thing l" , "Something valuable to have" , "one liable to be stripped?" , "Useful thing or person" , "Help" .)