You just don't get paid. I've had one vacation since 1991, when I sold the first book. I don't work 10-hour days anymore, which is nice. I do work seven days a week most weeks. And I never have enough time to do everything I want.
Creative control is great.
No caveats there. If your reward is the writing, though, even the long hours, the poor or nonexistent pay, and the anonymity will be no big deal. I've never known a successful writer who wasn't also a compulsive reader. The only real difference between the third answer to this question and the fourth is that some of us are book packrats, and some of us aren't. But if you aren't a big reader, you're going to have a terrible time figuring out what is a truly different approach to a story and what has been done to death.