Why start with a subject overview?
As you set out to research a topic, it's helpful to start with a broad subject overview. This gives you a sense of the context, background, and common theories/viewpoints in your field. For example, if you're researching a controversial issue, what are the major arguments on each side?
By reading a subject overview, you'll have a better understanding of how to continue. Think of it as an orientation on your topic before you dig in to more detailed and focused research.