We have it and so does my Mom (my Dad died in November

).
We live in a sue-happy world and the umbrella coverage is a great idea.
For example, my Mom (age 88) lives in a lovely assisted living residence just 4 miles from our house. Say she is walking down a hallway at the residence and accidently bumps into someone that works there. They fall down and are injured. They are covered by insurance through their job.
Now, say she is walking down a hallway at the residence and accidently bumps another resident, who then falls and hurts themselves. Even if the injury is not serious and they have medical insurance, they, and their family, could sue Mom (and US, by association) for a LOT of $$$ (mental stress, pain & suffering, etc).
Given that some folks in assisted living or nursing homes have dementia (which, can, in many sad cases, cause violent behaviour), a lawsuit could be even more likely if a loved one injures someone on purpose (because of the mental problem). *POOF* There go the life savings of, possibly, more than one person.
Mom's umbrella policy covers her for $1.3 million dollars, which would offer her a great deal of protection, in the event of a lawsuit.
Another example: If we hired some neighborhood kid to do some work around our property and he/she was injured, the same thing applies, they (or, their family) could easily sue us. The umbrella policy offers us some protection regarding the liability. This is one reason we don't hire anyone that isn't bonded and insured to do anything for us, and never ask friends for help with moving heavy items or doing anything else that could prove hazardous. It just isn't worth the risk.
If you can afford it, get it.