Well if any of you supply your product to your local dispensary, ask them what happens when you flush?? I've recently talked with mine, the herbal garden in Tacoma WA, and they do lab testing, and see what is left over in your bud after you harvest, trace minerals, heavy metals, etc. And they totally promote flushing. By using a flushing agent, florakleen, superleach, you can actually leach out impirities not just from your soil, but actually pull trace amounts from the plant.
Flushing is also great if you tend to over feed. If you feed heavy, your goign to get a build up of some sort of micro/macro nutrient in your soil, or medium, and if you flush, its like refreshing your soil back to new.
I have absolutely no science to back this up. But i trust what the pharmacy says!