Usefulness is universal in glen (5)
I believe the answer is:
value
'usefulness' is the definition.
(I've seen this in another clue)
'universal in glen' is the wordplay.
'universal' becomes 'U' (film certificate).
'in' is an insertion indicator.
'glen' becomes 'vale' (both can mean a type of valley).
'u' put within 'vale' is 'VALUE'.
'is' is the link.
(Other definitions for value that I've seen before include "Monetary worth" , "Appreciate" , "Hold dear, regard highly" , "Consider to be important" , "Assess, put a price on" .)