An encyclopedia can give you a solid background or introduction into a topic very quickly, and it can easily lead you into further topics and further sources. While most professors will not want you to cite encyclopedia articles in your papers, you might very well wind up citing the books and articles to which encyclopedias lead you.
Remember that you can also use the library's Database page and choose a subject, and get access to subject-specific encyclopedias. A lot more subject-specific encyclopedias can be found, print as well as online, using the library's OneSearch tool.