I have one. My wife and I were in our 50s when we met, (1) there's a big difference in our net worths, and (2) she has kids, I don't.
Her kids and I are aren't particularly close, didn't really want my estate going to people who were essentially strangers. I did however want to make sure she was provided for should I go first, she also wanted to be able to remain in our house (it's in my name, something I owned before we met).
One of her sons took a major financial bath when he got divorced...he owned several rental properties (again, purchased before he and his ex met), but never did a prenup and in his state they were considered community property.