One of the beauties of bookcraft is that there are no rules. Bookbinding is a little more rigid in its requirements. Since my scribblings here on BusyBusyDotCo are aimed at bookcrafters rather than binders I must be quick to point out ~ as the sub heading says ~ you do not have to work in eights of anything ~ nor fours ~ nor sixteens ~ nor quarters. No rules ~ just be inventive to suit your needs.
So why all the prattle? For many purposes printers ~ designers ~ bookbinders ~ are being very sensible when they work in 2~4~8~16~32~etc. Much of the World also works in these ratios ~ although they do not realize it.
As the printing press developed the printers realized that the tedious job of inserting paper into the press could be reduced if jobs could be printed 'two-up' ~ two separate tasks onto the same sheet. This applies today. A busy printing works may receive 500 different jobs in a day. Overnight their computer sorts them into suitable bundles such that customer A's handbills can be printed at the same time as customer B's sales literature ~ Customer C's letterheads can be printed at the same time as his compliment slips (provided the requirement is for twice or three times as many slips ~ it can all get pretty tricky. Invariably this 'ganging together' meant two ~ or four ~ jobs could be run at the same time.
This was especially the case with books ~ and much easier since the same number of pages are required ~ to the same size ~ on the same type of paper. If two pages could be printed side by side ~ and back to back ~ then the book is being printed with four pages in one pass. If the press was large enough then four pages are printed on one side of one sheet and four on the reverse ~ eight in one go. It was not uncommon for sixteen or thirty two pages to be printed at once. For many years that was the way a book was purchased. The pile of sheets representing the book were passed to the bookbinding works chosen by the customer. The gentry 'buying' the book would dictate their requirements to their chosen bookbinder who would bind in the required style. It was not uncommon for every book in the library to be bound according to the owner's taste ~ in the house style if you wish ~ although that term is now usually reserved for the design and layout of a book in the first place. I read somewhere that Lord Someone or other had all his fiction books bound in green Morocco, and the reference books in brown ~ or somesuch arrangement. Just as his tailor ~ and shoemaker ~ had all his measurements and tastes on file.
The reason printers worked two~up or four~ and so on ~ relied on the convenience of folding ~ or cutting ~ the printed sheet back into the required size. This is easily done ~ without measuring ~ by folding in half ~ and half again ~and so on. Sometimes it was necessary for economy of paper to print six-up. That does not present a problem for the printer ~ but it makes the finishing more difficult. You may sometimes find a book with half a dozen blank pages at the end ~ what a waste of paper! But it saves a ot of time to treat the odd number of pages left over at the end of a book in the same way as the rest of it. Authors are not required to work in chunks of sixteen pages.