Most Wii discs contain a partition with a system update. To save space, NKit removes these. To rebuild the ISO later, you need a library of these updates stored in your NKit folder.
Unlike "scrubbed" ISOs, NKit preserves the integrity of the data. nkit 1.4 fully loaded
While the Dolphin emulator can play .nkit.iso files directly, having the fully loaded toolkit allows you to convert them back to raw ISOs for use on original hardware via USB loaders, which often have better compatibility with raw formats. How to Use NKit 1.4 Most Wii discs contain a partition with a system update