P,
If you look at all the main SWCG's from Pentair, Hayward, Jandy, and all the others that I know of, their installation instructions are very clear that the SWCG's controller cannot have power when the pump is shut off. Although the SWCG's flow switch will keep the SWCG off if there is no water flowing water from the pump, it is a secondary safety device. The primary safety device is the timer, relay, or switch that prevents power from going to the controller if the pump is off.
The risk of relying only on the flow switch is low, but there is still a risk if the flow switch should fail in a closed position.
I run my SWCG 24/7, but most people do not. But running 24/7 does not mean that you should not have a timer on the SWCG. In my case, I have an automation system, the controls the power going the SWCG system.
Each pool and SWCG is different, so you need to set the % of output for what your pool needs. The longer you run the pump, the lower your % of output on the SWCG can be. This time a year my normal recommendation would be to run the pump for 8 hours and set the SWCG to 50%.
You can then adjust the run time or percentage to increase or decrease the amount of chlorine being generated.
Thanks,
Jim R.