Quoted from CUSTOM PC Magazine:
Scratched CDs and DVDs have several uses, coasters being a favourite, closely followed by frisbees. Retrieving data from them however, is generally out of the question, so it's best for all concerned if they don't get scratched at all. Enter the d_skins. These are plastic covers that can be snapped onto a DVD or CD to protect the surface of the disk from scratches. The bonus is that the disc is still readable with the d_dkin on, so once you've put them on you can forget about them being there. It's a lifesaver if you're the sort of person who has a habit of leacing CDs and DVDs lying around on your desk/floor/bag and yet still relies on them working.