Dog is initially big benefit (6)
I believe the answer is:
basset
'dog' is the definition.
(type of dog)
'initially big benefit' is the wordplay.
'initially big' becomes 'b' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'benefit' becomes 'asset' (I've seen this in another clue).
'b'+'asset'='BASSET'
'is' is the link.
Can you help me to learn more?
(Other definitions for basset that I've seen before include "Short-legged hound that hunts hares" , "Beasts (anag.)" , "Sturdy hunting dog" , "Short-legged hound used for hunting (6)Short-legged hound used for hunting" , "GAME" .)