You also have to realize that "flushing" is a broad term that means different things in different situations. In hydro/soilless flushing means running massive amounts of clean water through the medium to remove all salts, nutrients and everything else.. basically starting over. This can be done in soil, but the flushing will mostly remove additives and activate the soils own nutrients. Leaching, on the other hand, is commonlyh called flushing and this is basically just switching to pure water instead of nutrient water (without the flushing) so that the plant uses what is left in the medium, be it coco, rockwool, soil or whatever, and then begins to feed on itself - which results in the yellowing of leaves. Timed properly you can have the plant use up all the nutrients and harvest it just as it runs out and begins feeding off fan leaves... but in the end I'm not sure if it matters or not.