Instead of just aiming to deck an opponent out, mill payoffs let you turn every lost card into an advantage that pushes you closer to victory
There can also be some shenanigans regarding making absurd amounts of tokens if you have a strong enough board but, again, thats just how the game works
While they're both situational tools that may not be useful in every matchup , they have enough potential to warrent a spot in the deck
PGR Premium Gold Rare Nibiru, the Primal Being X LIGHT Level 11 [ RockEffect ] ATK 3000 DEF 600 During the Main Phase, if your opponent Normal or Special Summoned 5 or more monsters this turn (Quick Effect): You can Tribute as many face-up monsters on the field as possible, and if you do, Special Summon this card from your hand, then Special Summon 1 "Primal Being Token" (Rock/LIGHT/Level 11/ATK ?/DEF ?) to your opponent's field (this Token's ATK/DEF become the combined original ATK/DEF of the Tributed monsters)
The SR-or-above slot breaks down as: ~55% Pokemon SR, ~25% Supporter SR, ~15% SAR, ~5% UR