Shaped CDs or LPs are an invention made for collectors and labels aswell. To generate more money from one single release of a band it’s common practice to release different editions. The regular release, a special digital release, country specific releases and special collector’s editions. They often have extra tracks, a booklet with way more pages, content and pictures and sometimes come as shaped CDs.
Depicted above is Dimmu Borgir’s Alive in Torment shaped CD. The other examples are Dismember’s Death Metal, Statovarius’ I Walk To My Own Song and Machetazo’s split with Marrow on silver vinyl with red splatter in a sawblade shape.
Data can only be recorded on sections of a shaped CD that form uninterrupted circular tracks. Other parts of the shape are purely decorative – but are still often finished to the same appearance as a CD. They appear silver and reflective on the data side of the CD, even though they contain no actual valid bytes and cannot be read (source).