Imagine walking from your garage, into your kitchen, through your living room, outside to the pool and never missing your favorite lyrics from your favorite song because every room (inside and out) access the same centralized audio source.  You can opt for iPod, satellite radio, HD radio, music server, CD, etc.  All of these devices can be controlled from keypads throughout the house.  Also, different sources can be accessed in different rooms at the same time.  Pandora radio can be playing in the living room while the iPod is playing on the outside patio.