OK time to set some things straight:
When compressing GC games, dolphin just compresses the image sector by sector. This means no data is changed. This also means that you will only see space savings when the game has compressible areas; if the disc has real dummy data - which is to say that it is just random bits, and is not listed in the file table - then that area won't compress well.
On the other hand, Wii images are almost fully encrypted, so the data appears to be incompressible. To get around this, dolphin calculates which areas of the disc are not used in the filesystem, and fills them with 1s. This makes the unused areas extremely compressible. (The "scrubbed" image is then compressed in the same way the GC image is, above).
People have problems with the SSBB image because they download the "DVD5" version. It's not dolphin related.
When compressing GC games, dolphin just compresses the image sector by sector. This means no data is changed. This also means that you will only see space savings when the game has compressible areas; if the disc has real dummy data - which is to say that it is just random bits, and is not listed in the file table - then that area won't compress well.
On the other hand, Wii images are almost fully encrypted, so the data appears to be incompressible. To get around this, dolphin calculates which areas of the disc are not used in the filesystem, and fills them with 1s. This makes the unused areas extremely compressible. (The "scrubbed" image is then compressed in the same way the GC image is, above).
People have problems with the SSBB image because they download the "DVD5" version. It's not dolphin related.