The WBFS format was specifically designed for the Nintendo Wii to store game backups on external hard drives or SD cards. Unlike standard ISO files, which are a fixed 4.37 GB regardless of the game's actual content, WBFS files are . This means all the "garbage data" used to fill up a physical disc is removed, leaving only the essential game files.
Just Dance 2015 for Wii: Everything You Need to Know About the WBFS Format Just Dance 2015 Wii Wbfs