PNG Smoothing

Hey there, simply im thinking of replacing all the Vector graphics in a game with PNG versions for optimal performance, now as my game involves lots of rotation with trig etc i enabled smoothing on the image properties which cancels out the pixelation that you get when rotating bitmaps. But it seems to good to be true, is there a catch? Smoothing is as bad as Vector images or somthing :pac:!! PLz enlighten me!