I run my exhaust 24/7. I may adjust the power level manually depending on the temps. I’m veg I usually keep a screened vent open to bring in fresh air. With the power on low, not much air is coming in with no vents open. More negative pressure than anything if you as me.
I have a heat mat in there now covering the floor to keep the root zone from getting too cool/cold. I don’t worry about humidity. I’m as low as 20% in one tent, and 40% in another. “Swings” are what I’ve noticed will mess with a plant more than being out of ideal vpd range. Some may have different results. I tend to get lucky. Seriously lol