Please support game developers by purchasing official re-releases where possible (e.g., Nintendo Switch remasters).
This is the gold standard for console play. It "scrubs" the ISO, removing the "junk data" (random padding used to fill the disc) and update partitions. The Result: A game like New Super Mario Bros. Wii shrinks from 4.37 GB to roughly How to do it: Wii Backup Manager highly compressed wii games
Practical Workflows & Tooling (6–8 pages) highly compressed wii games