The primary goal of legal research is to efficiently find primary mandatory authority on your legal issue. Secondary sources are often the best place to begin your research because they include:
(1) references to primary authorities (statutes, regulations, and cases), and
(2) commentary on primary authorities to help you understand a specific area of law.
Secondary sources can be particularly useful when researching an area of law that you don't know well. They help you develop search terms to find primary authorities (the law), and help you put your legal issue into context. There are many types of secondary sources to consult, including:
Sometimes when you start your research by doing a keyword search for case law (or other primary authorities), you find too many cases to sift through in the time available, or too few cases that are relevant to the situation you're researching, or no case law results. Secondary sources can help in all of these situations.
Before you rely on a particular secondary source, keep in mind that its usefulness may be limited by its currency and comprehensiveness.
Because the law can change quickly, it is easy for a secondary source to become outdated. Always check the publication date of the secondary source you are consulting and update the primary sources it cites to ensure that they are still good law.
A secondary source may not include everything necessary for your analysis. You must not rely solely on the commentary found in a secondary source, but carefully read the primary sources it cites to determine if they are on point for your precise legal issue. Secondary sources are a beginning, not an end point.
Also, remember that secondary sources are always persuasive and never binding on courts. Secondary sources are most often used for background, context, and help locating the strongest primary authorities. Secondary sources should not be cited when trying to persuade a court, if binding authority (such as a relevant case decided by a higher court) is available.