For centuries, books were paper of some sort. There was no other sort of book. The paper was made with pulp from some sort of plant. Before easily made movable type was available, books were copied out by hand, or each page was carved from wood and they were printed. In fact, the word manuscript literally means hand-written.
Even after printing became easier, books were still written by hand. Every revision and draft was re-written by hand. Can you imagine waiting for, say, the next book in the Harry Potter series if J K Rowling had to write every draft of every 500+ page book by hand? Those 500 printed pages are single-spaced. Most manuscripts are double-spaced, to give room between the lines for making corrections. One page of typed, double-spaced text is roughly equal to two pages of hand written, single-spaced text. Most of my manuscripts go through two major revisions and four to six minor ones.
Mark Twain was the first author to write a manuscript on a typewriter, for which his editor was probably very grateful. My grandmother was a writer, and typed her things with three sheets of paper and two of carbon paper in the machine. If she made a mistake even on the last line of the page, she had to re-type the entire page.
Writing always has taken a lot of paper to produce a book, but that is changing. I write with my computer. If I make a mistake, I back up and it automagically disappears. My computer keeps track of all the changes I make. It can put it back the way I had it in the first place if I decide I don't like it. I can carry a hundred manuscripts on a flash drive in the palm of my hand.
Working on Tanella's Flight, we printed out the manuscript at each stage, using about a ream of paper. We sent printed copies to no less than fifteen readers. We probably went through at least two cases of paper preparing one book for publication.
Fabric of the World was only printed once before publication. Your eyes and brain process information differently when you read on a backlit screen and when you read on paper. We had to print the manuscript once to read it on paper, and find the last million mistakes you never notice on a computer screen.
With Deadly Gamble, the book was written, revised, read, and checked without being printed out even once. We did the final "paper test" with an ebook reader. When you're reading on an e-ink device such as a Nook or Kindle, your brain processes it like paper. People who buy an ebook copy of Deadly Gamble will get a book that has never been printed on paper. We think that's pretty awesome.
We still offer print copies for people who don't have, don't want, or can't afford an ebook reader, and those who prefer paper books. It's certainly easier (at the moment) to get a paper book autographed. We are not against paper books; we have a huge library full of them. We still think it's absolutely cool to be able to produce an entire book without using a single piece of paper!