Understanding what an Umbrella Policy is and what it does is a little easier than determining just who, exactly, needs one. Truthfully, the insurance agent’s answer, in the days of ever-increasing litigation, should be "everyone". Offering an Umbrella Liability Policy to insureds is something agents should be doing even to protect themselves against possible Errors and Omissions claims; insureds (you) should be made aware that Umbrella Liability coverage is available to protect your business or personal assets in the event of a third party claim.
Still, some insureds view the offer of Umbrella Insurance as an attempt by their agent to "up-sell" them coverage. When your insurance agent is offering you an umbrella policy, it should be made very clear to you that this is an optional coverage, albeit one that is highly recommended. Once it is established that the ball is in your court, it is important to look at your insurance needs objectively to properly determine if an Umbrella Liability Policy is indeed coverage you need.