If someone wrapped their hands around your neck, pinching off your ability to breathe in 100% of the needed oxygen, would
you grow to
your full potential? Plants are the same way; their photosynthetic processes use CO2, thereby creating oxygen. And though the plant does use some oxygen (in the roots), most of it's work comes from the CO2. Unfortunately, our atmosphere doesn't contain nearly as much CO2 as a plant can utilize.
Plain and simple: CO2 is a breadwinner. Your plants will vegetate faster, grow larger, and produce more weight than without. I do have pics of my grow using CO2, however, there's no plants that are not in contact with the CO2 for you to compare to, so it's hard to see the contrast.
This is my grow with CO2.
Take my word and get it. You won't be sorry.
-AR