I’m sometimes asked by people “if I have an executor named in my Will, why do I need a power of attorney?”
I like this question because the answer is easy, and isn’t “it depends” like many answers to legal questions are.
An agent under a power of attorney is someone who has the authority to handle your finances and property, and sign their name in your place while you are alive. Their power ends at your death.
An executor under a Will has the authority to handle your property and finances after you have passed away (and after their appointment has been affirmed by the Court.)
The duties of an executor and attorney-in-fact (what the person you appoint in your Power of Attorney is called) are very similar, but one has the authority to act while you are alive and the other has it after you have passed away.