Turning a reflowing book into fixed pages
The EPUB's chapters are read in their proper reading order and written out as a PDF you can print or annotate.
The order comes from the book's own manifest rather than from file names, so chapters arrive as the author intended. This is the conversion you want when a book has to become something physical or fixed: printing, marking up with a pen, submitting a document, or archiving a copy that will look identical on every machine forever.