The reason I said soreness is an indicator of an effective workout is because macrophage activity is the cause of soreness. The activity of macrophages triggers the release of anabolic hormones, specifically Testosterone, HGH, IGF-1, IGF-2, and certain prostaglandin's, that cause the anabolism of new tissue, and also are the cause of delayed onset muscle soreness (DOMS). The invasion of muscle fibers by macrophages is essential to the muscle growth process, because this is what activates satellite cells (stem cells).
Make sense?