Transmapped hair looks much more realistic than "solid" hair. As an example, you can see the difference between Kozaburos hair and the default Poser 4 "plastic" hairdos. The transmap makes the edges of the hair look like they do in real life: like an edge that gradually turns from solid hair to thin air. As an example you can try to render Kozaburos hair with and without the transparency map loaded. The different is obvious. I agree that the transmapped hair is difficult to work with, since it looks like a cloud of tiny dots until rendered. You can make it easier by turning transparency off in the material settings while working with it. Just remember to turn it on again before rendering :-)