Some random comments (from the point of view of the retail vendor)

Cardboard cases often don't have enough spine area to put readable titles. Can be a real problem if they're stacked in a bin with other CDs.

Odd shape and size are a pain in the patootie when it comes to mailing and packing.

Shrink wrapping, though not strictly necessary, makes a lot of cutomes feem more secure.

If you want to sell in stores, a UPC bar code and overwrapping are a must.

SLim cases are cheap, but don't have room for tray cards, which usually provide tracklists.