Kodak sells a special player for Photo CD in the consumer market. They also
sell licenses to companies like Corel to allow them to edit PCD files.
Multisession is important if you plan to add images to an existing CD. Each
time you add data, you create an additional session.
I don't really know why an ordinary consumer would mess with PCD, but
professional photographers (including technical professions like radiography)
can use this as a high-res archival and distribution medium. Kodak has
announced special products to support the more high-tech users such as
ultra-high-res images and special workstation-class editors.