Multi-language audio files, 4K pre-rendered cinematics, or update data.
However, a community plugin called was in early development in 2023, aiming to mount a compressed folder as a virtual filesystem using LZ4 block compression (fast decompression). It was abandoned due to sync issues with PPU threads. Unless a new contributor revives it, do not expect compression support in the next 2–3 years. rpcs3 highly compressed games work