On the positive side, these contributions give you future Medicare and Social Security benefits. If someone falls in your retail store and wins a big judgment against your retail company, structured as a sole proprietorship, that judgment is also against you as an individual. All of your personal assets are at risk. For some businesses, that is acceptable. For other businesses, it is not.
Partnerships also offer little liability protection for entrepreneurs.
Corporations are considered separate legal and taxable entities from the owners of the corporation. Shareholders own the corporation. Employees render services for the corporation. You will likely be both a shareholder and an employee of your corporation. If you are an angel investor in a company, you might be a shareholder without being an employee.