Benefit from experience, as it happens, with large gain (4,3,5)
I believe the answer is:
live and learn
'benefit from experience' is the definition.
'live and learn' can be an answer for 'experience' (I've seen this before). I'm unsure of the 'benefit from' bit.
'as it happens with large gain' is the wordplay.
'as it happens' becomes 'live' (as in live broadcasting).
'with' becomes 'and'.
'large' becomes 'L' (eg in clothes sizes).
'gain' becomes 'earn' (synonyms).
'live'+'and'+'l'+'earn'='LIVE AND LEARN'
Can you help me to learn more?
(Other definitions for live and learn that I've seen before include "Profit from experience" , "Keep finding out new things" .)