What exactly is being gained — and lost — in this commonly accepted practice?
"Under normal growing conditions, when nutrient availability exceeds demand, plants will store nutrients. When availability is low, they will cannibalize older plant material, robbing NPK and magnesium, and moving them to needy growing points.
Think about that. Flushing causes nutrients, especially nitrogen, to be moved into the buds to support growth. So although growers aim to remove nitrogen from the buds by flushing, the plant concentrates nutrients in the buds from other places in the plant. These nutrient concentrations are less than if the plant were nourished during the flush week, but concentrating less in the plant biomass is entirely different than removing nutrients from the biomass."