I'm sure that PoolSean will pitch in here, but as he has said in the past, an SWG is "slow and steady". If you don't maintain the CYA, then the SWG has a hard time keeping up with a demand spike.

I think of the higher CYA as a way to "bank" the CL produced by the SWG for when it is needed. Even in superchlorinate mode, it isn't like dumping in a couple of gallons of bleach after a pool party. There are many people that run their CYA at a lower level than recommended by the manufacturer and a lot that run at the low end of the range (I do myself, but that is still 60ppm).