They bake hundreds of cookies with different quantities of ingredient to show the effect that each ingredient has in the baking process. So now not only do you know what somebody's recipe is, but you also know exactly how to modify it to suit your own tastes.
This is why I really like Food Labs. This cookie recipe is the most famous example: https://www.seriouseats.com/the-food-lab-best-chocolate-chip...
They bake hundreds of cookies with different quantities of ingredient to show the effect that each ingredient has in the baking process. So now not only do you know what somebody's recipe is, but you also know exactly how to modify it to suit your own tastes.