Books and reference material are useful for getting an overview of a given topic.
For reference materials this overview is usually a short, fact oriented description of the topic, occasionally with references. They are considered one of the most authoritative sources.
Books, similarly, usually approach a topic from multiple perspectives. These are some of the longest forms of research, and you may find that you only need a specific chapter or section of a book, rather than the whole thing.
Keep in mind, a book can go the complete other direction in terms of specificity. Rather than an bird's eye view of a topic, it could delve very deep on just one aspect of a topic, exploring it fully and providing a deep understanding. Again, it may be valuable to focus on sections of books rather than complete works while doing research.