Your gonna get mixed reviews I like to keep mine on do some grows doing both ways and see which one works best for u cause everyone has a different environment
Keep in mind that if you shut off your extraction fan your carbon filter stops doing its job. If you don't want other people smelling your grow my advice is to leave it on.
I leave my air circulation fans on 24/7. I leave my tent pretty much open until about week 3 (no smell in early veg), then I close it up and flip on the exhaust fan and carbon filter. It stays on until the end.