Closed Air or Open Air System?

Im wondering what is better? Closed air system, or an open air system? I was told by my local hydro shop owner that a closed system is better..... Well does that mean that there is no fresh air coming into the room? Or does the CO2 replace the fresh air? There is no air exiting so I was gonna get a Can Fan Scrubber for the room itself, with its own AC. The lamps are being cooled by an outside source, Coiled to each hood, connected, and vented right outside. Thanks ahead of time

Ideally you want a sealed room capable of venting, intake/exhaust. With a couple of elec dampers that are normally closed and a couple inline fans, you can have a sealed room and still vent.....