From an audience perspective, archiving is similar to deleting — a visitor won’t be able to access the page. Archived pages will eventually disappear from Google search results, though it may take several days or weeks for that to happen. The main difference is that archived pages display an “Access Denied” message when someone tries to visit them, while deleted pages show an “Error 404: Page Not Found.”
From a CMS author perspective, deleting permanently removes the content, while archiving allows you to keep it temporarily in case you need to restore or reuse it later.