As PP stated, if you have assets that need protecting, then yes, you need one. We had a huge eye opener a couple of years ago. A guy on a motorcycle hit my 16 year old DS's car. Ruled motorcyclist's fault at the scene, but he was really hurt and rushed to the ER where he stayed for a couple of weeks. Motorcyclist hires high powered attorney and fought for over a year to have the fault for the accident switched to my DS so that he could sue us. We had a $500,000 liability limit on his auto policy, but that was not enough to cover the motorcyclist's hospital bills.
We found out that since we do have assets, we would be responsible for any damages over the $500,000 that State Farm would cover. We now have $1,000,000 in coverage for every driver in our family. In the end, the motorcyclist did not succeed in flipping liability, but it was a very stressful time for our family - the not knowing is the worst.
You think it could never happen to you, but in a blink of an eye you could be on the hook for hundreds of thousands of dollars of medical bills for someone else
We will never skimp on insurance again.