Question

How does the long coastline benefit India ?

Answer 1

the long coastline provides good space for ports.this can improve trade
fishermen have advantage

Answer 2

there are many benifits .
if you look in history it acts as a protection from invaders . it is a great supply of unlimited resorses and food ; its also a great trade centre 
the acient kings of south india used their sea power for prrotection and built up large navies . 
now also the country has many benifits on it for example ..salt prodution,fish trade etc