I've used both with campden and without. When I am able to acquire cider and process/pitch the same day, I don't do anything to it, and it turns out just fine. If you pitch a proper amount of healthy brewing yeast (use one of the online pitching rate calculators) it easily overwhelms any wild yeast and/or bacteria.
There have been some years where I've not been able to pick up the cider on the day the LHBS presses it, so they sulfite it and store it in one of their walk-ins for me until I can get it. I've not noted any taste difference, fermentation difference, or other side effects of the addition, but from my experience it isn't a necessary step if you can press and pitch immediately as noted...
Packaged: Dark Munich Citra SMaSH, Mayan Stout, Caramel Quad, Basic Spiced Cider, Spur of the Moment Graff
Recent Meads: Mead Day '11 Ginger Metheglin, Mead Day '12 Traditional (orange blossom) Mead, Fresh Simple Cyser '12, Cherry Melomel, Belgeglin, Bochet
Secondary: Why do I keep this line here...?
Bulk Aging: Cocobochet
Planned: Hop Metheglin #3 (NZ hops), Trad. Gesho T'ej