Everyone needs a Power of Attorney and it is one of the core documents executed in addition to a Will.
Essentially, it gives someone the power to take care of your stuff if you can't. Of course, we all see mom and dad losing their ability to monitor their finances, invest their assets and file their tax returns as they age. But what about you. What happens if you are in a car accident, are travelling abroad, or have a major operation.
Moreover, you can set up the Power of Attorney so it can't be used unless you are incapacitated.
If you don't have a Power of Attorney and you are incapacitated, then someone will have to start a Guardianship proceeding in court to handle your affairs.