cacheAsBitmap help

Ive been playing with Flash 8 latley particularly with the filters, but I would love to see cacheAsBitmap working.

The way I am implementing it is:

var myMovieClip:MovieClip = this.attachMovie("point","point",this.getNextHighestDepth());
myMovieClip.cacheAsBitmap = true;

I dont see any improvment in performance on large content movies. Am I doing something wrong?