Then there was the pocket (mass-market) paperback.
Then there was the high-quality "trade" paperback.
Then there was the audiobook.
Then there was the e-book.
Publishers looked for a way to deploy these different formats in order to maximize profits. Not unreasonable. In general, they believed that either paperback format would cannibalize the hardcover. So would e-books, if priced less than the hardcover. Audiobooks not as much of a problem as long as they were priced appropriately.
Also, they found that a paperback release about a year after the hardcover created a new marketing opportunity.
What they did not realize is that by postponing release of paperbacks, and in some cases e-books, they were squandering their best marketing opportunity. The one that comes when the book is new.
A consumer who hears or reads about a new title and gets excited, but is among the majority of readers who will not pay $25 for a book, is unlikely to remember that interest a year later, and unlikely to be reminded by a renewed marketing effort which in nearly all cases will have weaker results than the original campaign.
The most consumer-oriented and profitable approach in today's world of insta-demand is to publish every format simultaneously (including the decision on whether to even have a hardcover edition).
Kevin Smokler has a great piece in this week's Publishers Weekly on this subject. More than ever before, making consumers wait is a losing strategy.