Pages people write: private notes, shared spaces a team writes in together, and the documentation a record owns, like a project's handbook kept beside the project.
For the team that keeps its handbook in one tool, its meeting notes in another and its specs in a shared drive. Here a space holds pages, private to you or shared with the people you add. A project or a deal can own a space of its own, so its specs and notes open from the record they belong to rather than from a folder somebody has to find. Every page keeps its revisions, and a new one can start from a template.
Each of these points at Documents instead of keeping a copy of its own, and says what for.