PS3 ISO games read faster and have a better compatibility than JB games (less black screens).
PS3 ISO may also have better fps and less audio delays (due the faster read).
PS3 ISO can be played from almost any device type (FAT32, NTFS, exFAT, internal HDD). On FAT32 you need to split the ISO.
ISO format let you play games with files larger than 4GB directly, while JB games need to cache the split files .666** to the internal HDD.
If your JB game already plays fine there is no need to invest time converting it PS3 ISO.