A power of attorney can cover almost everything relating to the life of your loved ones and elderly parents to varying degrees, including (but not limited to):
Real Estate Transactions
Financial Decisions
Gifts
Asset Management
Medical and Healthcare Decisions
Guardianship
In essence, the agent in a power of attorney can make decisions on every major facet of their loved ones life (or principal's behalf). Because of this, the agent must be chosen with care - it should quite literally be someone that the principal trusts with their life. Especially with a medical POA governing health care.