Using any type of decomposing organic material (shrimp/prawns as well as the most popular: fishfood flakes) to cycle a tank has been around for decades. This is basically one of the systems that was more or less replaced in the modern hobby by the Fishless Cycling technique. When organic matter decomposes, what's really happening is that heterotrophic bacteria are using its materials and breaking it down into ammonia. The main problem with this for preparing a tank is that it is generally slow (its a whole extra step prior to having the ammonia) and even more than that it is very unpredictable and hard to control. Its very hard to get the amounts right. Its also very smelly!
Instead, controlled dosing of pure household ammonia goes straight to the step of growing the two needed species of autotrophic bacteria in the filter (Nitrosomonas and Nitrospira)
~~waterdrop~~