You can fit significantly more games on a single memory card. For example, a 1.2GB ISO might shrink to 700MB as a CSO.
: The format supports nine levels of compression. Higher levels result in smaller files but can lead to longer load times or "stuttering" in some high-bandwidth games. The PSP Archive Community Standards cso psp archive
: By archiving your library in CSO format, you can often fit twice as many games on the same microSD card. You can fit significantly more games on a single memory card