Protect yourself from a scenario where your "regular insurance" isn't enough. A personal umbrella policy is called an "umbrella" policy because it provides liability coverage over and above your standard auto insurance or homeowners insurance. It offers protection for you and your family against large and potentially devastating liability claims or judgments.
In short, a personal umbrella policy kicks in right where your other liability underlying limits have been reached. The more your earning power and assets increase, the more you have at risk, and therefore, the more you need to protect.