Well I'm talking about UV mapping and image application in general, not Poser specifically.

I'd have to take a look at those maps to see what you mean specifically, but by "ineffectively", to me that translates to "distorted".
Ideally, your UV shells should each be the same relative size as the polygons they correspond to. A UV map that has that done perfectly will be as effective and efficient and distortion-free as possible.

Then of course there's the issue of bending body parts and morph targets, both of which can cause texture stretching.