The study of typography is deeper than one would think. It is more than just picking a nice font for a project. The more you learn and understand the fundamentals and history of typography, the better you will be able to apply it to today's projects.
Type hierarchy is important in a page layout, as it helps the user understand levels of importance in the text and gives meaning to the message being shared. Hierarchy is also relevant to Section 508. When a web page is read aloud to a user by assist technology, the page hierarchy needs to be set up to work with these technologies in order for the page meaning to be translated correctly.
Depending on your role in a project, the expectations of the materials you are to provide to your clients or co-workers will vary. Once you choose your type selections and build your style guide, you may opt to go a step further and provide templates that use those choices. This ensures that the users of your materials have less setup and you have better consistency across a large project.