This is Actually Good, and I'd love more stuff written that way!
No, seriously. Just look what this example does - it recursively provides a short description for each of the important concepts in the process of baking cakes. After reading this, I now feel I have a decent map of the topic - both what the things / processes involve and what they don't involve. I've also been introduced to domain terminology that will help me understand other sources.
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As for original question, why definitions - I believe it's good to have precise definitions next to casual explanations of the same things, just so that the reader can quickly connect the casually discussed aspect with the precise definition, and answer some of their own questions (which authors can't predict) through thinking.