Your target TA is whatever results in your pH being reasonable stable. If your pH tends to rise over time, try lowering the TA to see if that helps. Usually with a pool using a hypochlorite source of chlorine, a TA of 80 ppm is about right, but saltwater chlorine generator pools may need something a bit lower. If you were to ever use an acidic source of chlorine such as Trichlor tabs, then the TA should be higher to compensate (for short term, it doesn't need to be higher, but for longer term it would).