Well thats like saying why bother having a personal ringtone on a mobile.
Granted a ringtone has more use than a flubber animation but its just another way to personalise an xbox.
My main reason is I want to insert a message to insult my mate when it starts up, as a joke.
Then I would just like to have my own sound in there.
I know you can stop the animation starting up but when I do that it still takes a while for the xbox to boot, so I might as well leave it in and have it play my own sound while I'm waiting.