It increases the player's luck attribute, which is used in loot tables.
There are a few couple values that a loot tables can include to specify how luck will give more loot or better loot. However, in Java 1.21.11, every single vanilla loot table specifies them such that it isn't affected by luck. The only exception is the fishing loot table, and it looks like that might be intended for supporting the Luck of the Sea enchantment.
So yeah, unless you want 2% better fishing loot... it's useless.
