Someone who has a very limited area to keep a computer in. Someone who doesn't want the clutter of having the computer seperate from the display and the extra cable(s) that would be in use, including a second power outlet. (Although I strongly recommend that computers be kept an good surge supressors.)
The iMac G5 takes up less desk space than a MacMini plus screen. Come to think of it, the iMacG4 is pretty effecient on desk space as well.
Remember everyone has different needs and esthetics.