Michigan's no-fault system pays your own medical bills through your own policy, which leads people to assume the other driver's insurance does not matter much. It matters a great deal the moment an injury is serious.
What it pays
Uninsured motorist (UM) and underinsured motorist (UIM) coverage steps into the shoes of an at-fault driver who cannot pay. If you are seriously injured — the legal threshold in Michigan is death, serious impairment of body function, or permanent serious disfigurement — you can bring a claim against the at-fault driver for pain and suffering and for economic losses beyond no-fault benefits. If that driver has no insurance, or carries only the $50,000 state minimum, your UM/UIM coverage pays what they cannot, up to your limit.
Why the limit should match your liability
People buy $250,000/$500,000 of liability coverage to protect others from their own mistakes and then leave UM/UIM at $50,000 to protect themselves. That is backwards. Whatever you have decided a serious injury is worth when you cause it is what it is worth when someone causes it to you. The premium difference between minimum UM/UIM and matching limits is usually a few dollars a month.
How it fits with an umbrella
Most umbrella policies do not include uninsured motorist coverage automatically. Some carriers offer it as an endorsement. If you carry an umbrella because you have a lot to protect, ask whether UM/UIM can ride on it.