Sometimes you are doing research for a project and you need to see what has been published on the topic. Let's say you are thinking about doing research on slave narratives from the Louisiana Purchase territory and you want to see if any scholarship has been published on the topic. You can use WorldCat to identify LC subject headings relevant to your project, as well as locate and identify rare books that might exist on the subject.
There are occasions when you will find the need to identify trends in publishing or compare editions of a work. WorldCat is an excellent tool for these kinds of tasks because it contains records from over 72,000 libraries. This can be an especially daunting task, as the definition of "work" and "edition" is not always.
Sometimes the bibliographic information for an item is incredibly important. Which edition was published first? Did this author publish this specific item before this other item was written or published? We all know how important citations are. You can use WorldCat to help sort everything out.