onClipEvent (load) : why?

My question why is do u need onClipEvent (load) in this, u can easily put it in the other statement


onClipEvent (load) {
trace("Hello World");
this._alpha = 50;
//this._visible = false
}


onClipEvent (mouseDown) {
this._rotation = this._rotation + 5
}


advFlash_20060615
clipEvents_01.fla