Why distributed audio??
Ever have a dinner party and want to play the same music throughout the home and outdoor areas?? Hope you like the radio....
You won't be listening to CDs unless you have several burned copies of each disc you want to play and you are exceptionally talented with syncing your mini-systems

OK, now why you would want multi-zone distributed audio...
Similare scenario except there's a sporting event (superbowl, olympics, world series, etc.) and the men gather in the media room to watch the event and the women gather in another area and couldn't care less. They guys can have the sporting event audio piped into the adjoining areas like the bar and maybe the closest bathroom so nobody misses out on the action. At the same time, the ladies are listening to the CD changer or music server in the other areas of the house simultaneously, and at different volumes room by room.

Another advantage...
All of your media can reside in a central location. When you want to listen to your old Eric Clapton CD, you don't have to search high and low in every room just to find it a few weeks later in the boombox in the garage where you left it when you waxed the car.

About distributed video:
As far as distributing S-Video, Component, RGBHV, etc... skip the baluns except to bail yourself out of a jam and use mini-coax penta cables and terminate them to a control friendly matrix switcher.
Extron, Altinex, Kramer, RGB Systems, etc. make several varieties and now companies like Key Digital and Audio Authority make more basic versions that will suit the needs of the residential system.
If you treat the system designed for today's need seperate from the "future proof" aspect of the cabling, you will be fine. Don't count on using all of those coaxes and CAT wires today, or you won't have anything left to expand with tomorrow.