Remember that you're not earn any money if you're not working. You don't have any employer benefit package, which means that it's going to be hard for you to go on vacation, take a day off, or even stay home sick without losing income. It also means that you'll have to provide your own health insurance and retirement plan. Beside, you will have less time for family, friends and yourself.
Because you're working for yourself, you're going to have to take care of everything yourself, from figuring your taxes to watering the office plants. You'll probably need some new skills, such as bookkeeping and filing quarterly taxes. You can learn to do these things yourself--many software programs are designed just for this market--or you can hire others (e.g., an accountant) to take care of them for you.
The owner may work for really long hours as well as weekends or holidays, and maybe there will be no vacations for years continuously. For instance, an owner will have to work until morning to read the reports, calculate the income, and prepare work for the next day.