In baking, proportions make all the difference. Take a cake, for example, the flour and the eggs, they function as the main structure-builders, holding the cake together; the sugars and fats do the opposite. They "wreck" the cake's structure, giving it tenderness and moister. As you can imagine, if you add too much flour or egg, your cake will become tough and dry. Likewise, add too much sugar or fats and your cake becomes a soupy mess. So how do you find the perfect balance? Professionals will tell you that the right ratio is the key to a perfect cake, no recipe required.
"When you know a culinary ratio, it's not like knowing a single recipe, it's instantly knowing a thousand recipes."(Michael Ruhlman) Ratios are loved by every baker because, not only do they eliminate the use of a pesky recipe, it also allows a baker to make as much or as little as they desire-simply by altering their ratio. In baking, all ratios are generally measured by weight rather than in cups, teaspoons or tablespoons. While ratios can be made using cups and the like, weights result in a more precise ratio as well as a better resulting product. However, bakers refer to the ratios as in "parts". "Parts" means that all the ingredients will be in the same measurements. For example, a cake is one part sugar, one part butter or other fat, one part flour, and one part eggs; or a ratio of 1:1:1:1.
As stated before, many bakers favor baking by a ratio as the recipe becomes more flexible. Also, with a ratio, one can easily substitute ingredients in and out of the recipe. Since ratios are solely whole numbers, they are super easy to commit to memory. Then, as one knows the ratios that make all kinds of basic recipes, one can modify them as they wish, creating all flavors of bread, cakes, and cookies. Through ratios one will find themselves no longer looking to recipes as instructions to bake, but rather as ideas for new kinds and flavors of products.
This page by Molly B. ('18)