Public Web resources have many useful types of information...

However...

Public Web resources generally do not go through a review process. Anyone can publish on the Web without passing the content through an editor. Pages might be written by an expert on the topic, a journalist, a disgruntled consumer or even a child.

Public Web resources are not organized. Some directory services, like Yahoo, provide links to sites in subject lists. But there are too many Web pages for any single directory service to comprehensively organize and index.

Public Web resources are seldom comprehensive. Rarely will you be able to use a search engine on the Web to collect information about your topic from earlier decades and different types of sources.

Public Web resources are not permanent. Some well-maintained sites are updated with very current information, but other sites may become quickly dated or disappear altogether without much if any notice.