The ability to permanently save a page with all content as a single, standard HTML file is huge for me. I save pages often, and don’t ever want to have to rely on some web site remaining up in order to read something later (e.g. with bookmarks.) Bookmarks are great if I think a page might be updated later, or I want somebody else to see it; but for saving “newspaper clippings” on my computer, nothing beats Save Page.
Save Page is also better than “scrapbook” or MHT plugins that use semi-standard formats that aren’t universally usable and often need conversion, or save pages as an entire cumbersome folder of files. Save Page created a single self-contained HTML file – 100% standard and universally usable.