IME you need to check a lot of things to grow colorful SPS.
I would say that PH is really not that critical that you have to test it everyday. Most of the time its just nice to know.
It's nice to know that its running pretty steady, and if you have a digital controller or moniter showing you what it is all the time, it can alert you to some other issue you might not know is happening. I will definately look into things if my PH is running abnormally high or low.
It becomes more critical to know your PH level for instance, if you are adding kalk, so that you don't OD and shoot your PH up to 10.0 for the day.
Or maybe if you are running your CO2 way to high on your CA reactor and plummeting your PH down to 7.0.