Reference librarians rely on such sources as excellent means for answering questions quickly.
Researchers will find sources such as the Encyclopaedia Britannica, which provides both concise articles on almost any subject and book length treatment of major subjects, invaluable as a starting point for learning about a subject. Thorough research should go beyond mere encyclopedic treatment into a more thorough search of both book and periodical literature. I am not suggesting that encyclopedias, handbooks, and yearbooks aren't valuable tools, only that they are by nature limited in the amount of detail they contain and in the specificity of their articles. The primary value of these irreplaceable reference works is their ability to provide basic information on almost any subject quickly. A good encyclopedia can provide a researcher with valuable guidance in how to approach a previously unfamiliar subject.