A SWG has three advantages over manually adding bleach. First it is added slowly over many hours. Assuming the SWG is running during the sunny part of the day the peak FC level can be significantly lower while the minimum level remains the same. A bleach feeder like the liquidator would have the same advantage. The minimum level is the one that really matters.
Second there is a super-chlorination effect that takes place inside part of the SWG cell which completely wipes out anything organic that goes through that part of the SWG cell. There has been a lively debate about the significance of super-chlorination. Since very little of the water gets the super-chlorination, some people think that it can't be that important. Unfortunatly there isn't enough collective experience with continuous bleach feed systems to measure the relative impact of the super-chlorination effect for outdoor pools. There is better, though still not conclusive, evidence that it can be significant in indoor pools.
Third, the SWG doesn't forget to put chlorine in. It is not very difficult to miss a day every once in a long while when manually adding bleach, at which point your FC level goes much lower than your nominal minimum.
In any case, experience has show that SWGs can run at lower FC levels than pools where bleach is added once a day. Which of the three reasons is most important is not really known.
