Some fields have certain restrictions and are not "open to the public", thus "PPR". The restrictions can run from type of aircraft allowed or only for local club members. The owner then decides whether he can allow you to come or not. It's his decision.
His field may also have a certain number of "non-local" flights allowed, i.e. max. 100 per year, so, if you're the number 99 he may also want to reject your request.
The fields may also have restricted opening hours due to neighbors, or there may have to be someone present for your landing and no one is available, then it's no-go. Another reason could be the grass being mowed, the asphalt being repaired, or other such stuff.
So, there may be times when they just say, "sure, come on over" and other times when they say "sorry, not today!".
PPR just means it's the owners discretion if he allows you to land or not.
Westy