Quick prawn curry recipe

I thought I would pass on the link to a (fairly) quick and easy prawn curry

recipe:

http://www.bbc.co.uk/food/recipes/database/keralakingprawnandco_75325.shtml

I've used it a few times now and it seems to be pretty good - better than 
you would think for such a quick recipe. I think the coriander blended
with 
the coconut milk is the key.

Anyway, I haven't used grated onion as required in the recipe. I've used 
(out of laziness) chopped onion instead. The result seems to be okay. What

would be the benefit of using grated onion?

Gareth.