Can you provide specifics where your feeling comes from?
CYA does two functions - buffers harshness of chlorine and protects chlorine from sun UV. Indoor water does not get UV.
SWG generate small amounts of CL over long periods of time. Outdoors a SWG is most efficient when you protect the CL being generated from the suns UV using higher levels of CYA. With an indoor pool or spa there is not that requirement.