I know some people use the pH controller to achieve the desired pH and kH level in the tank. But isn't that defeat the purpose of injecting CO2 for the plants to photosensitizing?
We add CO2 for the plants, not for pH control (directly).
In other words, it's not some specific pH plants prefer.
It's CO2 that they prefer.
I'd say one out maybe 20-100 people use a pH controller, mostly newbies that bought everything(like myself way back when), and then try and justify it after getting stuck with it.
I use a decent pH meter and use it a relative measure.
I add CO2 for one reason, for the plants and they only use CO2 during the day. So I add CO2 only during the day.