Giving somebody the right to act on your behalf and in your stead always carries a risk, no matter how small. If the person the principal chooses to be their attorney-in-fact cannot be trusted to act in their best interest, it can end badly.
The general rule is to only choose an individual who can be fully trusted to make the best decisions for the principal. Otherwise, the principal may suffer financially or even physically in the case of the medical power of attorney.