Well it's relevant because Jim Humble refers to it in his books as do lots of other Miracle-Mineral-Supplement sites declaring it as the reason Miracle-Mineral-Supplement boosts the immune system.
He thinks ClO2 breakdown helps produce myeloperoxidase but doesn't explain why he thinks this. I haven't been able to find a reason it should.
It supplies chloride ions which are used to make hypochlorous acid but they should be abundant enough anyway.