This shows two shells and two trajectories. "A" shows gun shrapnel, fired with high velocity and flat trajectory. These two factors cause the balls to fan out over a deep but fairly narrow area. Gun shrapnel was highly effective against men in the open, but much less effective against troops in cover or protection. "B" shows howitzer shrapnel coming down from a high trajectory. The arced trajectory limits the area covered by the balls, but also means that the balls can reach behind cover, such as a gunshield or wall. "C" shows high explosive shell penetrating cover. While clearly the most effective in these circumstances, it is also clearly less effective at covering open ground than shrapnel.
Source: H. A. Bethell, Modern Artillery in the Field