WBFS files strip away this useless padding, leaving only the actual game data. A game like New Super Mario Bros. Wii might shrink from 4.3GB down to just FAT32 Compatibility:
: A simple dedicated freeware tool specifically for converting WBFS files back into standard ISO format. Key Repacking Concepts RVZ to WBFS for Nintendo Wii on Windows
Open Dolphin Emulator. Click "Add New Path" and navigate to the folder containing your new .wbfs file. Double-click the game. If it boots to the title screen, your repack is successful.