In Evidence-Based Nursing, there are two types of questions that are often asked: background questions and foreground questions. Background questions are often asked by those who are new to the field or a topic and need to know what's already well-documented.
Books compile a lot of known information into one place to provide an in-depth overview of a topic. You often learn the history and evolution of topics and practices. Books are your primary resource as you learn the basics or need background information.