So, following on from that:
You decide to fly to the airfield where I work, not having phoned beforehand. You turn up to find a 747 blocking the runway doing pre-planned engine runs, which had you called before you would have known about.
Still think it's losing its meaning? PPR means just that - Prior Permission REQUIRED. If you phone and they're not interested in taking your details then fine - you've fulfilled your side of the contract. If you don't get an answer then you don't go - or you have a fallback in case you get refused.
(And Whirly knows this - a certain 'farm' if memory serves right?
)