The document discusses the importance of yield tests in determining: 1) The amount of food to purchase based on how much will be usable after trimming, cooking, etc. 2) The best form of an ingredient to purchase to minimize waste. For example, a whole fish may have more trimmings than a filleted fish. 3) The best cooking method to use. Some methods result in greater moisture loss and thus lower yields. Yield tests can show which methods are most efficient.