The new UMD media is really cool - fits in the palm of your hand and can hold a full length feature film or a PSP game. However, the read window is its greatest weakness. You don't want to touch the media and you don't want things getting inside of the case.
The UMD Cases in the combo packs can each hold one UMD and protect it from dust, grit and fingerprints. The folks at MadCatz know that you'll need more than one, so they give you a few to get started. Depending on the combo you choose, you'll get 6 or even 12 of these.