I did it becuase my baby was vomiting watery looking liquid (foremilk) in huge quantities all over everything and her poo was green-ish, very liquid and fizzy.
She also made a lot of clicking, gulping and choking sounds as she fed and having fed 3 children previously I knew that something wasn't right.
I searched for over actve let down on Kellymom, found block feeding tried it and it solved our problems.