Also what would happen if the PWD decided to do equity release on their home, to something special for themselves, or their family, or help a grandhild get on the property ladder with a couple of thousand towards a house deposit.
The way I've always looked at it is that the powers that be are not interested in micromanaging anyone's life. Ensuring that the PWD is paying their way, and that their POA has access to the funds to do that (including things like Attendance Allowance to pay for enhanced care/spending needs) is one thing. Nobody need fear being taken to task for that kind of financial management (as seems to be the case with the original poster).
But once dementia is on the roadmap, future care needs have to be top of the list of financial concerns for anyone with more assets. Giving the traditional £20, or whatever, to a grandchild at Christmas is one thing. Helping them with a house deposit is quite another, even if it's what the PWD would have, or still, wishes. It would be very easy for investigators to say that the PWD was neglecting to take their own greatly altered circumstances into consideration. And I imagine equity release would be a very risky thing to try to get away with... assuming it's ever a good idea for anyone other that the firms enabling it.
Of course if nobody ever complains and the Office of the Public Guardian never has cause to investigate, I'm sure anything's possible. But the more money involved, the more anyone with POA should check before doing anything. Ultimately we're 100% legally responsible for any mistakes, and ignorance is never an excuse.