I have read many posts stating that the SWG should be off during SLAM. The most oft stated reason is that you don't want to work your SWG that hard,
Having said that, I do run mine during a SLAM. I find that it makes it much easier to keep the chlorine level where it belongs. I don't think a couple of days in a year are going to make that much difference in the life of an SWG. My last SWG cell was still going strong when we moved after 9 years.
I bring it up to the level called for with liquid chlorine, then use the SWG as a buffer. I turn the SWG off at night before I check for my OCLT, then turn it back on after I check in the morning. The SWG can't bring the level up quickly and provide the shock you are looking for, so always add the required amount of liquid chlorine to shock it and bring it the level you need based on the FC/CYA chart.
I also find that with the SWG running, I don't need to check my levels every two hours - I only check morning, noon, and night. For me, I don't have to run it at 100% to maintain the level - usually somewhere around 50%-75% the first day works well, then I back it off the next day. It normally is done in two days.