Uninsured motorist is for medical coverage right?
I ask, because I have kick ass medical insurance and have zero need to be covered under an auto policy further.
It's simply asking your own insurance company to pay you the compensation that you'd normally get by suing the other guy who's responsible for inflicting the damage upon you.
If you're permanently disabled (in a coma or a quadriplegic) by someone, then you'd want compensation for your loss of lifetime earnings. Or if your spouse was killed in the collision, then you'd want compensation for that. At the very least you'd want the other driver to cover your complete rehab from your injuries, not just whatever kick ass medical insurance would cover. And finally, if their slamming into your car causes you to damage other cars/property, then you'd want them to cover that too.
My spouse and I are medically insured by Tricare, which is incredibly cheap and fairly good. Our daughter was only covered past age 21 if she was a full-time college student, and then only to age 23. When we were raising her, we carried uninsured/underinsured coverage to handle any lifelong disability or other problems inflicted on her by an auto accident. When she moved out and got her own job/insurance, we looked into cancelling our UM/UIM. It turned out to be a savings of only a few bucks a month, so we're keeping it.