Big creatures give you a commanding presence on the board that can be hard to overcome if your opponent is skimping on removal spells
This amount of damage kills the blocker
It can proliferate Lulu, Stern Guardian's stun counters, Fathom Mage's +1/+1 counters, and Protection Magic's shield counters, for instance
It is this insurance style of use that helps reduce random screws deciding games however it probably doesn't outweigh the increase of random wins from when it is being used in its intended capacity, the old turn one Mox, Slith Firewalker on the play used to be so good
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There's no limit on this, and where this is a problem is that anyone draws the cards, not just you, so this is strongest in decks that have self-sacrifice engines like Vampiric Rites