There is some thought that the triangles being smaller on a compact frame will create a stiffer frame that is capable of absorbing more rider input power without flexing. This doesn't necessarily result in a comfortable frame. Modern CF frames work more toward allowing some vertical compliance for comfort while retaining lateral stiffness.

My own opinion is that compact frames allow some more virtual top tube length without increasing standover height. While this may be good for riders such a Tom Bombadil and myself with relatively short legs and long torso's I'm not sure if the population in general will benefit.