My understanding of Advance Health Directives snapped into focus when I heard this NPR story. It’s a quick read or just over 7 minutes to hear the whole piece.

There are times when the American healthcare system will do anything to
prolong life, even beyond the point that many patients consider reasonable.
That is one reason why NPR ran a story about a town where everyone
makes advance health directives to decide for themselves how to be
cared for at the end stages of life. The results changed the entire health
care system and opened up frank discussions within families.

The most compelling part tells the story of a medical ethicist whose job is
to consult with family members of critically ill patients to make end of
life decisions. Too often the family members were asked to make decisions
without advance guidance from their loved one. Writing an advance health
directive gives your family members something to refer back to and take
direction from when it comes time for them to make decisions in your name.
More information is available here.