The only real explanation I've got for "flushing" a plant (starving it) is to induce senescence. This doesn't flush nutes, obviously, but it does, as claimed by the grower I heard it from, help break down sugars and chlorophyll in the bud before harvest. This is what, supposedly, causes better smoke. I know that this is what happens during the curing process, but maybe, just maybe, there could be benefit to doing this while the plant is still alive. The grower I've mentioned does a 10 day "flush" wondering if any of you who've really studied botany could chime in.