@Archimage It's integrated with blog hosting, so it's easier to post about your books and you can include them in pages. There's also a separate official app just for them: Epilogue.

I agree that the benefits of this should be made clearer, since it's not immediately obvious as to why it sits alongside the core Micro.blog set of features. There's also a Help article about Bookshelves on the forums, which is missing from the Table of Contents.