I'm not exactly sure, but here's my understanding of a PR Manager.
A PR Manager is the guy who kind-of advertises your game,and is in charge of selling the seats in an arena every game. Aside from that, he's the one who gives you the fan survey after every game. A PR Manager can have the National Appeal specialty, which lowers an opponent's home court advantage on the road, or the Crowd Involvement specialty, which increases your home court advantage at home.
A higher level PR manager will, if I understand correctly, provide a more accurate Fan Survey, usually higher results than a lower level, and because of the higher fan survey, the attendance will likely be slightly higher the next home game.
Hope this helps!
Clubcool
By the way, in the last two weeks, I think the National Appeal specialty has shown its worth, but I can't be sure, because I greatly overpower all but one team in the other league.