A Power of Attorney is a legal instrument that grants another person the authority to act as your legal representative, and to make binding financial and legal decisions on your behalf. A Power of Attorney can be "general" (unlimited scope and duration) or "specific" (limited powers), and can be revoked at any time by the person granting the power.
The most important reason to have a Power of Attorney is for a medical emergency or disability. An unexpected medical emergency may render you unable to make medical decisions for yourself and require you to rely on someone you trust to make those decisions for you. A Power of Attorney for Health Care, also known as an Advance Health Care Directive, provides a clear line of decision-making authority if such a medical emergency arises. A Power of Attorney for Health Care is usually included in one's Living Trust, but not always. You should check your Living Trust to see if it has been included and is updated for your current situation.
If your medical situation leaves you incapacitated for some time or your health is gradually declining over time, you may need assistance with financial matters like paying bills or depositing money into your bank account. In that case, a Durable Power of Attorney may be in order as it allows you to give specific powers to someone you trust to handle your financial matters.