Aftermarket performance flat tappet and roller camshafts usually have higher valve lift and require a higher than stock spring rate in order to control valve action. Stock rocker arms with ball fulcrums are not designed to be used with more than 300 lb. valve spring pressure. Grooved rocker balls will give you an additional 30 lb. open load but open valve spring pressure more than 330 lb. should always be used with full roller rocker arms. When using high lift camshafts, full roller rocker arms will reduce oil temperature, diminish side load on the valve stems which reduces wear on the valve guides. Tight valve guide clearances and the use of self lubricating phosphor-bronze valve guide liners will allow more accurate valve seating.
This is why full roller rocker arms should be used with high performance flat tappet or roller camshafts. GM came to the same conclusion in 2000 when they introduced pedestal mounted, roller fulcrum rocker arms and the factory ball fulcrum rocker arms went the way of the Do-Do bird.