One benefit worth mentioning about umbrella policies, is that if someone files a law suit against you, you get the benefit of the insurance company's lawyers that step right up and aggressively defend you. Kind of like having the best lawyers on retainer ready to defend you at any time. The premium is a small price to pay for this benefit alone.
This is true of your home/auto policies as well.
Not to belabor this, but the insurance company is in no way defending you.
They would throw you to the wolves if it benefited them in the slightest.
They are only "defending" themselves against paying out any settlements.
