Preview is inspection. Export is production.
Writing structure is not page structure
A section may need to exist in the project while its heading should be hidden in the book. A working branch may stay in the project while being excluded from output. Page breaks, cover, illustrations, and current versions only become meaningful when the whole book is assembled.
Preview creates a cheap failure
It is better to discover an accidental blank page, wrong heading, stale version, broken illustration flow, or awkward page break before generating and sending the deliverable.
Export has a destination
DOCX may be right for an editor, EPUB for an ebook workflow, PDF for a controlled reading copy, Markdown or TXT for another tool. Export answers “what artifact do I need now?”
assets/img/bmaker/bmaker-explained-preview-export-01.webpThe useful rule
Preview whenever presentation matters. Export when you know what you are producing and for whom.