A power of attorney is good to have in place in the event you become injured or are otherwise unable to handle your own affairs, whether you have personal, medical, or financial issues to manage.
In many cases, having a power of attorney can help you avoid the expense of a guardianship if for some reason you are no longer able to care for yourself or your finances.
A power of attorney can also be useful for people who are traveling and need someone back at home to handle financial or real estate matters for them.