The following is an article from The Mayo Clinic Published Nov 11 2014
Living wills and advance directives describe your preferences for end-of-life care. These documents speak for you when you're not able to speak for yourself.
Living wills and other advance directives are written, legal instructions regarding your preferences for medical care if you are unable to make decisions for yourself. Advance directives guide choices for doctors and caregivers if you're terminally ill, seriously injured, in a coma, in the late stages of dementia or near the end of life.
By planning ahead, you can get the medical care you want, avoid unnecessary suffering and relieve caregivers of decision-making burdens during moments of crisis or grief. You also help reduce confusion or disagreement about the choices you would want people to make on your behalf.
Advance directives aren't just for older adults. Unexpected end-of-life situations can happen at any age, so it's important for all adults to prepare these documents.