When the shortcut is worth taking
EPUB lets prose reflow to an ereader screen instead of preserving each PDF page as a fixed canvas.
What the shortcut cannot decide
Headers, footers, columns and page-positioned artwork can interrupt chapter flow when the source was designed for print. That boundary is why the source should remain available throughout review.
From source to result
The working sequence is short: prepare the uploaded PDF; process it as PDF to EPUB; inspect a downloadable EPUB file; then test it in the receiving application. Test navigation, chapter order, images, footnotes and font scaling in at least two EPUB readers.
Keep the master safe
Use fixed-layout output or keep the PDF when exact page geometry is essential to meaning.