When a publisher contracts for a book, someone in the proverbial back room builds a budget and plans a cover price. Costs are accounted for, such as for development- and copyediting, indexing, paper, printing, and binding. Price of competing books is looked at. A schedule is built. Deviating from the planned length unleashes a domino-effect on cost and schedule that can doom an otherwise excellent book.
It is surprisingly more common for authors to exceed their page-count than to come in low. Going over by 10% or 15% is generally fine – no worries. Even a 20% overage is seldom a problem unless the book is large to begin with. But losing control and failing to stay within reasonable bounds of the target unleashes a cascade of trouble:
There is a multiplier effect. More pages = increased developmental editing costs + increased technical review costs + increased copyediting costs + increased indexing costs + increased production and manufacturing costs. Many of these costs are incurred on a per-page basis.
Future revenue is lost. An acquisition/development editor forced to spend unexpected time on a book going over its planned page count suddenly has less time to create new projects and drive much-needed revenue. Jobs in publishing depend upon acquisition editors creating a steady stream of new projects.
Market opportunities can be lost. Do you want your book in print for an upcoming industry event? Is there a window of opportunity in which your book can be the only book on its topic? Will an impending new software release make your book obsolete? Books routinely fail on these points because authors lose control over their content.
Distribution costs can rise significantly. Forward-thinking publishers increasingly send digital files to business partners such as Amazon.com and Ingram Content Group. These partners print locally around the world in small batches using print-on-demand (POD) technology, but there are page-count limits that must be respected. (Currently the limits are 828 pages for Amazon.com, and 1200 pages for Ingram Content Group, for a typical computer book). Exceeding a limit by even one page closes off a distribution avenue and pushes a book into the next more expensive mode of distribution. The result is a sharp and unwelcome increase in cost.
Foreign markets can be entirely lost. It is one thing to transmit digital files to an overseas partner capable of printing and selling the book in a local market. It is quite another to ask that business partner to take the risk of buying and paying to ship (and literally in a ship too, because air freight is too costly for heavy books) a large quantity of books on topics that are time-sensitive, only to possibly end up with pallet-loads of out-of-date books good for nothing but the recycle bin.
Going long isn't the only problem. Coming in at too low a page-count carries its own set of damaging effects:
The ability to compete is affected. A 300-page book won't stack up well against a 500-page competitor, for example.
The value proposition is often damaged. You might lower the page count, but publishing management rarely agrees to lower a price from the original plan. The original price will stand, for better or worse; often it's for worse.
Let's not forget the added burden to the author when writing long. The act of writing is difficult and requires deliberate planning and an investment of time from the author. Many in the technology world write part-time, spending evenings and weekends away from family and in front of a lonely keyboard. Why increase that burden any more than needed? If 20 pages is the target for a chapter, then deliver the 20. Or deliver 25 if you must. Just don't quintuple your work by writing 100. Yes, I have seen it happen.
Higher costs from writing long force a publisher to reduce forecasted profit. A publisher forced to lower price due to a low page count must likewise forecast less revenue. One book coming in out of plan is not a huge deal, but still the effects must be acknowledged and dealt with. Wide variations from plan across many books can make it difficult for a publisher to maintain a stable, revenue forecast. Deficiencies in cost and revenue structures must be made up – one way or the other. Such is the reality of business. It must be so. The math is brutal.
What's the solution? Hold to your planned page count. Adjust your content to fit the space available. Doing so is part and parcel of being a writer. Any topic can be written to any length. Take responsibility for the length you promised to deliver, and deliver it! Warn your editor when a large deviation from plan is needed, and make sure it really is needed. Probably it is not needed, and you would do your editor a huge favor by rethinking your approach and scope so as to meet the planned length and deliver a product that can be sold into the market at the planned price, and with the planned cost structure.