In most cases, this is because you managed to knock out one of the stronger Pokemon ex, GX, Vmax, or any other Pokemon with a special ruling
Today, we're milling cards to beef up creatures with Aggro Mill

Academic Dispute Academy Raider Accelerate Akki Ronin Akki Scrapchomper Akoum Flameseeker Aleatory Amber Gristle O'Maul Ambitious Assault Ancestral Anger Arterial Alchemy Artist's Talent Ashling, Flame Dancer Ashling, Rekindled Axiom Engraver Balduvian Rage Battlefield Scavenger Bedlam Reveler Belligerent Guest Bestial Fury Big Score Big Wheel Bitter Reunion Blindblast Blood Petal Celebrant Blood Sun Bloodfire Mentor Bloody Betrayal Boiling Blood Boundary Lands Ranger Brand Brass's Tunnel-Grinder Burning-Tree Vandal Burnout Case of the Crimson Pulse Chandra's Defeat Chandra's Regulator Chandra, Spark Hunter Change of Fortune Chaotic Strike Charging Strifeknight Charming Scoundrel Clamorous Ironclad Cleansing Wildfire Cloudpiercer Common Iguana Conspiracy Theorist Cool but Rude Crash Through Crimson Wisps Cunning Maneuver Curse of Chaos Day of the Moon Decaying Time Loop Decree of Annihilation Deem Worthy Demand Answers Demonic Ruckus Desert Cerodon Desperate Ravings Destructive Digger Discerning Peddler Dismissive Pyromancer Dragon Mantle Drannith Stinger Electric Revelation Ember Shot Enthusiastic Study Epiphany Storm Exocrine Expedite Explosion of Riches

After all, why cast Mulldrifter just once for two cards when you could get insurmountable value by blinking it nine times
Finding the Value While the power level of the deck may not truly matter, there is one thing that all MTG players care about