If one has comprehensive coverage along with Liability ( Bodily and property), so why does one may need uninsured/under insured coverage for vehicle insurance if he already has Collision.
Some states require you to have uninsured motorist property damage insurance, so depending on your state you could just need it regardless of whether you'd otherwise benefit from it.
Uninsured/Underinsured coverage helps in cases of hit/run and in cases when the at-fault party is uninsured/underinsured. Collision also covers those instances, but typically does so with higher premiums/deductibles than uninsured/underinsured coverage.
My agent advocates going with a higher deductible on my collision to keep premiums low and keeping uninsured/underinsured insurance on the policy. So if I'm at fault I have to shell out a bit more, but if I'm not at fault there's very little out of pocket expense for me. This feels like a good balance to me. If you're already shelling out for a low deductible, it might not be worth adding uninsured/underinsured.