As a sole proprietor, if something goes wrong, your personal assets have no legal protection. You are personally liable for any mistakes you may make in your business, or any debts the business accrues. Banks may be reluctant to grant loans to sole proprietors, though this may not be much of an issue if, for example, you’re a consultant working out of a home office and don’t have much overhead.
Also, this may not be a suitable structure for a growing company or one that hires a lot of employees. But remember, you can always change structures if you outgrow your current one.