Main task that's easy comes as a blow on the coast (3,6)
I believe the answer is:
sea breeze
'easy comes as a blow on the coast' is the definition.
I can't judge whether this definition defines the answer.
'main task' is the wordplay.
'main' becomes 'sea' ('sea' can be a synonym of 'main').
'task' becomes 'breeze' (I have seen 'Simple task' mean 'breeze' so perhaps 'task' could also mean 'breeze').
'sea'+'breeze'='SEA-BREEZE'
'that's' is the link.
Can you help me to learn more?
(Other definitions for sea breeze that I've seen before include "Onshore wind; cocktail" , "that creates a cool ambience around 6 [ISLE] ?" , "Maritime wind" , "Gentle coastal wind" , "Doctor" .)