The easy navigation menu allows you to see the whole document structure from any page. You can create as many of these structures as you like; each individual page has its own access controls, so you can reveal portions of the structure while keeping others hidden. In keeping with all other elements in Elgg, you can add comments on a page, or search for pages by tag.
Pages really come into their own in two areas, firstly as a way for users to build up things such as a resume, reflective documentation and so on. The second thing is in the area of collaboration, especially when in the context of groups. With the powerful access controls on both read and write, this plugin is ideal for collaborative document creation.