get away with no exhaust in 3x3 mother tent?

ive seen DIY grows where people have basically just hung a light from the ceiling and put a plant underneath it so it just left in the open room .

im thinking of this but putting it in the tent for the mylar but leaving the door open and covering with a sheet when lights out . but keep vents open and a couple of oscilating fans

there is hvac in each room so the air in the rooms is filtered continuously

If you're not worried about the smell, no problem.. I keep my tent open all thru veg, then zip it shut and turn on exhaust during flower..

Depends on the humidity.

Recently I set up a new grow , did my usual tap into the chimney for extraction.

Didn't notice any issues till the plants had grown to like 16" .. then suddenly theres water running down the walls and dripping off the ceiling.
RH over 80%
Turns out the chimney was capped off .
Only just got it uncapped and now its alright.

What's the reason for not wanting to exhaust that particular tent?
I assume your other areas are exhausted?