A slightly different perspective on the the last paragraph that JVTrain wrote ...
I would think that there is an advantage of a SWG if the tub is used infrequently as the SWG should be able to maintain the FC levels for maintenance instead of requiring the addition of bleach every couple days even when not in use. But, you should likely not rely on the SWG to take care of your bather waste when the tub is used. I would think that after each soak, you should dose the spa with bleach as described in the link above and then let the SWG maintain the FC until the next time you use it.