The cookbooks I have I acquired thinking they were good sources of recipes, and they kind of are. But the real value I found, is the sections on "how to cook". Everything in those books on technique: from knowing how to convert tablespoons to volumetric ounces (yes, I'm American) to how to temper eggs. My favorite bread recipe book, for example, isn't my favorite because the recipes are the best, but because it taught me how to make bread, including things like creating a sourdough starter from scratch.

Recipes are easy to find, especially now with the internet.