For much of the 20th Century, writers composed both flops and masterpieces on 8.5 x 11-inch sheets of paper. Later they used word-processing software that emulated the same size and shape.
- Most authors have a specific word-count in mind, such as 70,000 words, as they write their books. (Apparently, the average book has 64,500 words.)
- But, as the owner/operator of my own tiny publishing company, when I'm working on a book, I usually have a specific page-count and price in mind for a pbook (Printed on Paper book), such as 350 pages and $15.95. Each piece of paper costs me money.
By viewing actual pages, it's much easier to judge my progress, and to know if chapters should be chopped, stretched or shifted, and when illustrations should be enlarged, reduced or moved around. [Pages shown are from my Stories I'd Tell My Children (but maybe not until they're adults), available as ebook, hardcover and paperback. You'll find lots of funny stories and a few murders.]
I always insert a temporary left-hand "page zero" ahead of the real right-hand "page one" so I can view pages as realistic two-page spreads, instead of onesies, or with left-right-reversals.
This is not very important if a book is all-text (or an ebook), but if you have photos or illustrations or tables, it's important to view the spreads as your readers will see them, to avoid graphic disasters.
I was copyeditor on my college newspaper in dreadful Bethlehem, Pennsylvania and often had to trim text to fit the page.
After college I was assistant editor of High Fidelity Trade News in Manhattan, and had to do the same thing.
Later I worked for advertising agencies and had to write to fit the available space (or available time for commercials). I couldn't tell an ad client to spend thousands of dollars extra to buy an additional page or 30 more seconds to contain my precious words.
If my background was in writing fiction or web pages or reporting for NPR (with no limits of space or time) my book production style might have evolved differently.
There are many different types of workflow for writers. Writers whose words will be formatted by others may work very differently than die-hard D-I-Yers like me. But, if your end-product is a book, consider making one from the very beginning.