Well, I don't know if my answers are 100% right, but it's my input:::

With CO2, the plant will grow faster during veg (not that you'll veg for 2 days...).
During flowering, you can get "nice" looking buds, to say the least.
With CO2, you are one of the few that run it.
If you run CO2 with ppm meters, controllers, exhaust fans, cycles, and such, you'll be the envy of your local chapter of Indoor Cannabis Sunday Gatherings Club,
If done right, you'll be very cool. Indeed.

But with CO2, you should run a/c to keep temperatures within check... unless you have a super-duper dialed-in grow/ventilation/light setup.

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Ventilation, well... it grows along just fine. Maybe it's less hassle... Ok, it's definitely less hassle.

......

Just my 4 cents.