Once a creature you control has become blocked, reducing its power to 2 or less and/or increasing the power of the creature blocking it to 3 or greater won't cause it to become unblocked
Yidris, Maelstrom Wielder harnesses raw chaotic energy to obliterate his foes, channeling the Maelstrom at Alara's center
For example, cards like Angel of Jubilation and Yasharn, Implacable Earth can be used to prevent an opponent Sacrificing their own creatures, and Tarjuru Preserver or Sigarda, Host of Herons stops foes from forcing you to Sacrifice creatures
The extra bonuses also fit into many Golgari strategies, especially food
Arms Of Hadar will have a spot in any deck that runs black, as it will shut down plenty of small, fast aggro decks