When people face incapacitation in life it can be a real challenge. People have to learn to rely on others in order for their most basic needs to be met. This doesn't just include people's basic needs -- like housing or food -- but it also includes people's financial affairs. Elderly people, in particular, may need help managing their finances if they begin to lose the ability to help themselves.
In order to do this legally many people create a power of attorney where they authorize another person to act on their behalf. This legal document can be narrowly or broadly constructed to serve the needs of the person.