A sole proprietorship is the default small business when you work on your own but you don't have partners and you don't use a business entity. The sole proprietorship has no liability protection. You, in your personal capacity, are completely exposed. Any lawsuit against your business may attempt to collect your personal assets and not just your business assets.
Operating as a sole proprietor is a last resort and is never recommended by this office.
However, please don't confuse the term sole proprietor versus an LLC taxed as a sole proprietor. The first has no liability protection, and the second does.