Though configuring TYPO3 Flow is very straightforward and pretty well documented, the Definitive Guide tells you more about how to configure your installation/package than telling you about what exactly you can configure. Here is where the Settings.yaml of the TYPO3.Flow package steps in.
Even though TYPO3 Flow, TYPO3 Neos and Fluid are pretty well documented you can get sometimes a little bit lost when looking for specific information. Especially the usability of the official TYPO3 websites is not really great, as the page structure is IMO not well thought-out. And not to tell about the search functionality, which is currently pretty useless in most cases (e.g. have you ever tried to search for a Fluid ViewHelper on docs.typo3.org? Not quite the definition of meaningful search results…).