PoA is also used whenever someone might be absent for a while. Whenever troops deploy overseas, they'll sign over PoA to a responsible individual who can do things like authorize big housing repairs, purchases, and all that stuff. Any thing that's authorized in the PoA packet is fair game for the named individual.

Sometimes 19 year old airmen sign over PoA to their wives who then go out and buy cars, jewelry, a deposit and payments on a rental property, and all that stuff before dropping a stack of divorce papers on their hubby's lap when they return.

So yeah, it's not just mentally incapable of making a decision, but can be done willingly and stupidly.