Issac...SWGs have been in use 40+ years

They have become more affordable and popular over the past 10-15 years. No one is arguing that it may not be the most economical source of chlorination, but it is a great option and helps you avoid lugging jugs of liquid chlorine around. Using liquid chlorine or the use of a SWG to chlorinate vs other sources (trichlor tabs/Dichlor/CalHypo) is by far preferred as it does little to affect other chemical levels in your pool.
As you mentioned either will not affect CH or CYA. Excess CH can lead to calium scale issues, while high CYA will overstabilize the pool.