When doing academic research, it is important to use high quality, credible, relevant, and authoritative sources. After all, the sources you use are a direct reflection on the quality of your writing. In order to ensure you are using these types of sources, you need to evaluate everything you use.
When using websites, the evaluation process is critically important. The World Wide Web is rich with information to help you research almost any topic; however, not all of the information you find there is useful or reliable. After all, anyone can put up a website or upload a document to the internet. They don't have to be intelligent or knowledgeable, and more often than not the information does not have to be checked for accuracy or edited for content.