One scholar draws on, responds to, or critiques earlier scholars' positions and ideas. Writers cite the earlier works to show readers exactly what they're using. The chains of citations form a web. In law, the web extends from academic literature to the law itself when judges cite scholarship as persuasive authority.
Researchers care about this web of sources for different purposes, e.g.:
Different tools give you different pieces of the picture. There is no one tool that quickly and efficiently tells you everything that cites a given work. For instance, one tool might give you a good display of U.S. law journals that cite a work, but not journals from other academic disciplines. This guide explains different tools and their strengths and weaknesses.