A corporation is the most sophisticated--and protective--form of business organization.
It is a "legal person," completely separate from the individuals who own and control it. A corporation has the power to do anything any person may do: carry on business, own property, lend and borrow money, or sue and be sued. Most important, it offers its shareholders limited liability: its stockholders can lose no more than their original investment; they are not liable for the debts of the corporation.
Although limited liability may be the most attractive feature of incorporating, there are many others. For many people, there is greater ease in doing business. There are a few drawbacks, but they're mostly minor ones. There will be more paperwork, and you will have to set yourself a salary and live within it. There will be a greater number of taxes to pay, but your total tax bill will be much lower than it was as a sole proprietorship---especially if you live in states or cities that impose taxes on unincorporated businesses.
Depending on the state you live in, your business or profession may require you to incorporate as a "professional corporation," but this means only that your professional practice is now able to enjoy all the benefits and privileges of corporations that had earlier been prohibited. There is no difference in the tax treatment of professional versus business corporations; the only difference is a legal and supervisory one. If you form a professional corporation, all the shareholders and officers of the corporation must be licensed as professional practitioners in the state of incorporation.
In terms of the law, a professional corporation is more restrictive in structure than a general business corporation. If your state permits you to choose, it is better to incorporate as a general business corporation. But whatever you do, if you are earning enough money and want to shelter substantial portions of it from taxes, you should consider incorporation.
It's pretty clear that the advantages far outweigh the disadvantages, and that's why more and more people are following their lawyers' and accountants' advice and incorporating.
Source: Judith McQuown: Inc. Yourself, 11th Edition: How to Profit by Setting Up Your Own Corporation