They give concreteness to abstract concepts and show students what I'm trying to describe. The downside to this process is that creating these stacks prior to class is time-consuming. Text has to be typed in. Those video portions which are to be used have to be preprogrammed, as does the music. Clip art has to be sought out and placed.
Buttons have to be created.
The upside, however, is tremendous. In addition to the more theoretical advantages mentioned, there are some very practical ones. For instance, stacks can be saved on floppy disks. This allows students who were absent, or who learn at a different pace, to see the lecture without me. Also, the stack is ready for use next year, and can be very easily modified to suit changing circumstances.