Every writer will tell you that writing a book is a long, slow, and sometimes painful, business. The ground is never solid, the foundations are always shifting, and the book that hits the bookshop shelves can sometimes be a slightly different beast from the one you had initial envisioned - especially when the dreaded editor gets involved.
You see, things often change between the first and second draft - often between other drafts, too - but not quite as dramatically or (at times) extensively as after you've delivered that first draft. Sometimes it's only minor changes, like the odd sentence changed here, the odd paragraph cut there, but sometimes it can be a biggy - like a whole chapter being removed.
It can also be the other way round - things being added, expanded upon between drafts,
Take, for example, a script I delivered only the other day - the page count for the first draft stood at 47 pages, and even when I attached it to the email and clicked 'send', I knew that things were missing, that certain important elements still needed to be added. When I attached the redrafted script to the email a day or two later and clicked 'send' the page count now stood at 59 pages and two new scenes had been added, one introducing a character who will become enormously important to the story that unfolds in the following two episodes.
Sometimes the things you cut are obvious - they either slow down the pace of the book, or take the story off at a strange tangent, or just don't sit right in the story as a whole. More often than not, passages cut from a book are at the request of one of the people - either the editor or the author - seldom are they fully agreed upon by both.
The below chapter - taken from the first draft of my Star Trek book Shadow of the Machine - was cut between the first and second draft as it was thought that the device that the young James Kirk was using was a little too similar to a modern day iPad and therefore might be a bit ditracting. I was sad to see it go originally, believing that it added a vital aspect to the character of Kirk and explained some of the later actions and dialogue with his nephew Peter near the end of the book. But, upon reflection now, I think it was probably the right choice.
This chapter originally followed the scene where Kirk, Peter, Hanna and Abner, all sitting down to dinner, begin to argue and Peter storms out.