By the very nature of the outline—that is, its built-in indentation of various levels—you can see at a glance what the main ideas are, what subtopics are related or subordinate to each of those main ideas, and some supporting and minor details. The indentation provides visual cues as to what information is most important, what the hierarchy of the information is, and how various concepts are related to one another. This makes your notes easier to understand later, as well as easier to remember and visualize when necessary. You can see how much harder this would be if you made everything look equally important