AFAIUI, it's not really NECESSARY in regards to the actual plant biology. It's more about keeping odor out of places you don't want it. What you don't want is TOO MUCH negative air pressure. As long as your tents walls aren't rigidly sucked in you should be fine. My tent walls slightly suck in but I can easily move them back and forth so what you want is SLIGHT negative pressure. Just enough so nothing really escapes.
I have the ACI T3 on backorder. It's supposed to ship in mid May. Can't wait until it gets here. I currently have an ultrasonic that works fine but having to manually turn it on and off when it goes out of range is annoying especially when their are products like the ACI humidifiers that can take care of that without you having to intervene constantly.
What I've noticed with my lights and tent is each light adds around 4 or 5 degrees to the ambient air coming into the tent. My lights are 275w quantum boards. I have 2 in the tent......with one more 150w on the way(thanks
ViparSpectra!!!) and my lights off temps hover around 70* and with them on my temps hover around 75* - 80*. My tent is located in a small office as the lung room and has central air conditioning so home temps are around 72* - 73*.