Boros Dwarves swarms with cheap creatures (Dwarven Mauler, Warden of the Inner Sky) and equipment, making Slagstorm's 3 damage to each creature a strong sweeper against their early board before Leyline Axe or Basilisk Collar come online. Spell Pierce is a proactive way to stop their key equipment on the cheap while we develop our engine. Spell Snare whiffs on most of their curve (their cheap cards are mostly creatures at 1 mana that dodge exact MV2, and Kili the Resourceful/Leyline Axe cost more), so we cut it along with Get Out, which cannot bounce opposing threats and cannot counter their key equipment.