Well, part of the problem is that a lot of these subdivider functions will transform a flat surface into a very gradual curve, thus using about 120 polys to display what previously took 2 if you over do it, and makes your model look overweight if you under do it, so the side of an orion not only starts to look 'curvy' but uses up a much larger number of polys.
As far as smoothing groups are concerned, never even figured out what the were to be honest, I makes the ships, bung em through PCS, chuck em into modelview for other little bits and away you go, or more commonly, debugging you go!

Flipside

Edit : The worlds shortest modelling tutorial
