It can be as general or as specific as the grantor wishes. Useful, for example, in the case of a grantor being out of the country. Can either be within a power of attorney or a separate document. Done to give family members and physician guidance. It is more general than an advance directive.
People are superstitious.
They feel they'll be tempting fate. Don't have several family members gang up. If they seem reluctant at first, don't push. Try again another time. Maybe you should think about it too.