For me it will take alot of stress of temps, odor and security off of me. I am setting up 2 4x4 sealed rooms and if my chiller works out good than it wont really run that much to maintain temps with a 30 gal rez.
If I run it open I still have to run blowers, dehumidifier, maintain a lower temp and provide fresh air, to me that takes alot of effort, electricity and is a pain in the ass to keep dialed in when the seasons change. Once you get a sealed room dialed in the environment never changes unless you want it to and you can put all the effort into growing. Just my opinion and its also difficult when working with a budget. By adding Co2 should increase productivity and outweigh the additional cost of electricity if your looking to increase yield.