Why not use plain old pure ammonia?

Pure ammonia among other benefits lets YOU decide how many nitrifying bacteria will develop during the cycling process. In other words you cycle according to your stocking plans and you are always sure about the outcome.
With the other method you can't control the rate at which a dead shrimp will decay, you can't control how much the fish will poop and most importantly you can never be sure that these fish (or shrimp) have no parasites.