I’m not well qualified since I am able to grow without needing extraction fans but the main purpose is to hide the smell of your grow from your neighbors. They use a carbon filter to scrub the air. Some larger ops may use a lung room before or after the grow space and then scrub and vent that air to outside. Most get by with passive intake just an open but screened vent(s) in the bottom of the tent to draw in fresh cool air and then exhaust the warm air out scrubbed or not scrubbed depending on each growers setup. Environment is he last leg of the trifecta, great genetics, great light & great environment. Temp, rh & airflow look up a VPD chart in search box here, VPD is one method to dial in a grow