Assuming you’re new to card games: Pot of Greed draws two cards, which is a huge advantage. “Card advantage” is an enormous factor in all games like YGO, MTG, Lot5R etc.. More cards in your hand means more options at your disposal, and more information/less mystery as to what will emerge from your deck next.

There’s no real cost to deploying Pot of Greed, and for the cost of one card you get to draw two more. Generally speaking, when building a deck you want it to be as small as possible for a focussed playstyle and to eliminate the effect of randomness aka low info. “Milling” cards help with this, by essentially filling a necessary card slot (decks must have a min size) while letting you quickly draw more cards to access the rest.

In a no-bans YGO format (which would be insane but anyway), you could include 3 Pots of Greed plus a whole bunch of similar cards like Jar of Greed, the angel spell that I can’t remember the name of, the Solemn Judgement or whatever trap and some others. Each of those is essentially a “vacuum” card that exists to fill a slot, but which once drawn will have no purpose but to suck up one or more other cards from the deck into your hand. Effectively you can skip the random drawing of potentially useless cards part of the game and get straight to the hand full of good cards with a coordinated and prepared strategy phase for little to no cost.

Personally I don’t give a shit about any of this because I can percieve roulettes / ROQ (random outcome qualities) for what they are which is softcore gambling or craps, aka the outcome of the match is unrelated to player skill, info or ability, so I don’t mind if either side of a match skips past this. But the games rely on randomness to draw matches out and keep things uncertain, so within that flawed framework the Pot of Greed and similar cards are way OP.