Layout and images for me are the most important. So if typed it in would still need to scan the images and correct for the layout, easier to scan and be done with it. Yes the text searching is a massive bonus, using the index if it has no errors is ok.
Most important and i have seen many badly scanned documents and books.
The need to have the whole page flat as possible and aligned for scanning, not easy everytime, without dark shadows.
Maybe someone works in a copy shop, do they have copiers now that don't require a book to be spread wide open for copying, or splines shredded ?