A Page takes a chat answer out of the scrolling conversation and gives it a home of its own. A normal Copilot Chat reply scrolls away as you keep asking questions. Added to a Page, it sits on a persistent canvas where you can edit the text directly or keep prompting Copilot to extend it. Pages keep a version history, so an edit that goes wrong can be undone by restoring an earlier version.
The bigger difference is that a Page is shared work. You can share it with colleagues and co-edit it live, the same way as a shared Word or OneNote document, and anyone on it can keep chatting with Copilot from inside the Page. A Claude artifact is the closest equivalent, but it is not built for that kind of live co-editing.