The attorney has a duty to act in your best interests and take care in managing your affairs.
A power of attorney is valid only if you, the person giving the authority, have capacity to deal with the matters yourself at the time you make it. Is commonly used if you are overseas or if you are physically incapacitated.
Most people appoint a family member or close friend as their attorney. The person appointed must be at least 20 years old and have legal capacity but cannot be bankrupt.
You can cancel a power of attorney by revoking it in writing at any time and notifying your attorney.
If you become mentally incapable the power of attorney may be void unless you provide for it to continue in those circumstances.