When making bread, one needs an incredibly small amount of yeast to begin the process. In fact, if you know how, you can collect the right kinds of yeast from the skins of any kind of fruit with a "blush" (such as plums or various berries). In the biodynamic preparations, something similar occurs. It is almost as if we are trying to culture specific yeasts of primal creative power. The same "leaven" that generated the planets we are seeking to concentrate in the biodynamic preparations to restore to the Earth what has been depleted from human exploitation.
You can see this approach in indigenous agricultural traditions where specific foods are given over to nature and allowed to transform in specific ways. Korean Natural Farming (KNF) resonates with some of the biodynamic methods in the great care produced and the microbiological diversity cultivated in the soil.
The biodynamic preparations work a bit like specialized "yeasts" in compost and create a better final product. Are the biodynamic preparations absolutely necessary? Of course not, or agriculture would never have sustained itself without them. But as the splendid book Farmers of Forty Centuries demonstrates how agriculture can be sustained on the same plots for vast periods of time. Biodynamics seeks to be a merely a humble supplement in the vast tradition of regenerative agriculture. Biodynamics works well with any number of regenerative models, and is compliant with certified Organic farming. Biodynamics is not an ideology anymore than taking a multivitamin (in itself) means you need to become obsessed with your health.
Biodynamics is a fertile hypothesis that can be tested yourself and at relatively little cost.