CYA is a bit of a balancing act, the more you use the less chlorine you need to use, but the more likely you are to have complications. For normal pools CYA at 30 to 50 is a good balance between the advantages and the disadvantages. Adding a SWG changes two factors that affect this tradeoff. First the SWG makes it much less likely you will need to shock the pool, significantly reducing the chances of complications due to high CYA. Secondly the SWG lifetime is very dependent on how much total chlorine you need. Higher CYA levels mean less chlorine used and thus a longer lifetime for the SWG. These two factors shift the balance so that higher CYA levels (70 - 80) work better with a SWG than they would without.