After sacrificing Zack and sending him to your graveyard instead of your command zone, reanimation effects like the one on Sun Titan can bring him back into play or to your hand to restart the gameplay loop , allowing you to keep stacking counters on your creatures
Its particularly potent when cheated out via reanimation effects, too, or cards like Sneak Attack
However, it becomes excellent when paired with Mufasa, Betrayed Leaders ability, The Sun Will Set, which means that when this card is banished players can reveal the top of their deck and play it for free if its a character
However, neither the price you pay nor our recommendations (or lack thereof) are impacted by that
By making them both uncommons that green-black was happy to play, the cost to put them in your deck was low enough that you'd take them both, and then it's time to Ragnarok and roll