With DIY CO2 you could have too much surface ripple, since you can't increase the CO2 bubble rate, the amount of CO2 in the water will decrease. With pressurized CO2, you can always increase the bubble rate to compensate for the loss of CO2 from having lots of surface ripple. Surface ripple increases the surface area of the water, so it increases the amount of O2 dissolved into the water from the air. Having more O2 dissolved in the water is always good for the fish, since it makes it easier for them to live with the CO2 in the water. Growing plants do supply some O2, but most of it in the water comes from the air-water interface.