It allows the emulator to read the data without high CPU overhead.
If you are playing on an original GameCube via a GC Loader or SD2SP2, the "Swiss" homebrew software supports compressed formats like NKIT and specialized shrunk ISOs. gamecube rom highly compressed
Compression techniques strip away this useless padding, leaving only the essential game files. Top Compression Formats for GameCube It allows the emulator to read the data
Developed specifically by the Dolphin team, RVZ is currently the best way to store highly compressed GameCube ROMs. gamecube rom highly compressed