First of all, a living will is not a will.
A living will and power of attorney for health care are both types of advanced directives: a legal declaration of how you want future medical decisions to be made should you be unable to make that decision yourself. Both documents, in essence, force caregivers to give you the specific treatment you want even when you cannot communicate that choice. Advanced Directives are drafted earlier in life, when you can fully understand the choices you are making (capable) and jump into effect when you no longer can understand those choices (incapable).
A health care power of attorney authorizes the trustworthy person of your choice to make medical decisions for you, based on the preferences you stated in the power of attorney. People often choose a family member, close friend or their attorney to act on their behalf.
A living will entrusts the medical preferences you dictated within the document to be followed by a doctor directly rather than electing a family member or friend to speak on your behalf. Also, while a power of attorney can go into effect at anytime you are incapacitated (ex: having surgery) a living will is ONLY for using, withholding or withdrawing life-sustaining treatment (to pull the plug or not to pull the plug). The living will becomes effective legally when you are determined to be permanently unconscious or brain damaged by a certified physician.
The power of attorney document is more flexible as it is not confined to terminal conditions, like the living will. Also, the power of attorney can either direct the agent to follow their specific instructions or to use their own best judgment based on the circumstances. While a living will only addresses issues relating to the postponement of your death, the health care power of attorney can address all types of issues, including life-sustaining treatments.
By making these end-of-life decisions ahead of time, you save your family the difficulty, confusion and burden of making life and death decisions during an already emotionally tumultuous time.
For more information, check out the Chicago Tribune article, "Help with End of Life Plans" I am quoted in: http://tinyurl.com/yzbmpfn