I currently am just finishing up 3 Purple Frostbytes, flowered in a 2x4 tent, i also have 20-30 plants and clones vegging in a 4x4 tent. Im coming up on harvest in a couple weeks, i have not used a carbon scrubber from the start. My house has a faint light odor of cannabis, but not enough to smell anything outside around the house. The only way youd possibly know is if you walked past the door to the room the grow is in. I live alone in a small house, so i dont have to worry about anyone smelling it, but im moving the whole grow to my basement because when my family visits, or friends come over it definetly smells like weed in my house. I smoke 24/7 so everyone who comes in assumes its from that, but if you live in a appt, or have sketchy neighbors or family coming around i would get a carbon filter. Its in my plans, just have better things to purchase first, like more T5's. Goodluck, and shelling out a bit of cash to cover your ass from losing everything, including freedom and your grow, id go with the filter.