This simply means to maintain a greater proportion of leaves compared to stem. However, maximum digestible nutrient yield almost always occurs at or before flag leaf. Yield per acre increases as tillers grow, but mainly yield increases as the number of tillers per acre increases. New tillers are produced in response to several actions. Generally, removal of top growth will stimulate tillering, as long as the basal bud is protected.
Proper fertility is needed for maximum tiller development, as is reasonable moisture.
Energy is used by the plant to develop new tillers. This energy comes from carbohydrates stored in roots and the lower stem bases. The new tiller uses this stored energy to 'feed' the new growth until it develops enough leaf area to produce its own energy or food from the sun by photosynthesis. At that point the depleted root energy is replaced. Depleted root energy reserves slow new tiller development.