In the referenced thread in the original posting, there’s an excellent excerpt from the Diocese of Pittsburg on the subject, and that covers my take on the subject.
As it notes, widows and widowers seem the most probable users of these documents, for the sake of children of their now ended marriage. And depending on where you are, merely putting something in one’s will may not be enough because of the marriage laws of the jurisdiction. For example, here in Canada, each Province and Territory has marriage laws, and one of them, Quebec, has laws that find their origins in the Code Napoleon (as does all of their civil law, Quebec being the only province with a civil code). I would be very leary of an agreement that sought to protect assets from the intended husband or wife, but to protect them from the government or the laws it has passed, oh yeah, you bet! We’re long past the days when governments were friends of marriage.