As hard as it was for me to believe this before I got published, being contracted to write a book based on a paragraph or two or a chapter or so (I've done both) can be kind of a pain, which I think is what you're getting at here. It's nice to have the publisher's commitment (such as it is), but it can sometimes feel like you're writing with a straightjacket on. The security might feel nice, but I'm not always sure it produces the best work.