While cards like these are valuable in helping you maintain your hand size and not run out of cards to play, they alone arent enough to get you a significantly bigger card selection and to allow you to play many powerful cards that dont replace themselves with a new card in your hand
POKMON CARD GAME sv1S 099/078 Super Rare card
Shirei is worded in a way that lets you loop Creatures on your opponents' turns too, so with a free sacrifice outlet you can get triggers from cards like Bone Shredder, Dusk Legion Zealot, or Abyssal Gatekeeper
The cards, generally speaking, can function all right in and of themselves, but because of this synergy, produce more together than what they could when taken in isolation
See how delightful
BPhillipYork: This can be broken, there's way to create mana enough to blink this, Dockside Extortionist is an obvious huge mana generator here, but there's also Su-Chi and other sources, you could also do something like sacrificing Gnawing Vermin or Stitchers Supplier and generate a lot of mill, if you were into that sort of thing