A power of attorney is a legal document that lets you choose someone to act for you or on behalf of you in certain situations, such as when you are ill or unavailable. Thus, the nominated person becomes the agent or attorney-in-fact to act on behalf.

Power of Attorney acts in the period you think you might not be physically or mentally available.The extent of responsibilities and access can be decided by you in a legal document

Example:
It is common for people with large assets who might be sick or in their old age to choose a power of attorney. This is different from choosing a beneficiary since your inheritors only get to manage your finances after your death.