Boros Aggro wants to curve out with cheap threats like Momo, Sarkhan, Dragon Ascendant, and Voice of Victory, so Seam Rip can exile one of those mana value 2 or less permanents before it snowballs, denying Momo's cost reduction or Sarkhan's treasure engine. Pyrrhic Strike can also destroy a bigger threat like Magmatic Hellkite (mana value 4) or Nova Hellkite (mana value 5), since both meet the mana value 3-or-greater requirement for its creature mode. That mode works without paying the optional blight 2 additional cost, so you don't need to put two -1/-1 counters on one of your creatures to use it. Liliana the Faultless's 1/1 body dies instantly to their aggressive creatures and Burst Lightning, and Essence Channeler isn't needed when answers to their fast clock matter more than another small body. Stabilize quickly with lifegain to outlast their burn-heavy aggression.