Wikipedia is a popular resource for a good reason. It provides overveiws of topics that are new to us and serves as a quick source of well-known information. However, like any source of information, it has its limitations that come out of its format. There are issues of both accuracy and bias in Wikipedia.
Encouraging students to look beyond their well-known reference source lets them know that there are other options and encourages the use of a wider variety of information sources when conducting research.
Other reference sources for background information: