I hate homework - advantages actually depend on the components installed vs the ones upgraded. Generally speaking higher capacity, faster speeds, less heat, greater compatibility (in the case of ide vs sata as many new boards are coming with less ide connections if any at all) For cd - dvd or blu-ray of course greater compatibility across more media, the ability to use said media, dvd/bluray add more storage capacity over a cd.
Health risks, electrocution, respiratory issues from dust, potential cuts from removing the case (IDK sounds good tho)