If you use the Poser 4 renderer, you need high poly. Without displacement and smoothing you are just too limited. If you use smoothing and displacement, the meshes can be much smaller, without a loss of quality.  To demonstrate the differences - the picture is the poser 4 casual woman with an instant breast magnet. One render with smoothing, one render without. The P4 renderer obviously needs more polys.

Does smoothing increase the rendertime? Probably, if you smooth everything. I try to switch smoothing off on everything which doesn't need it - but I really like to have the option. I don't think that the Firefly renderer is crap or something - just more complicated and with lousy preferences. But since a lot of people still use the P4 renderer, models still need to be high-poly, I suppose.

A ship in port is safe; but that is not what ships are built for.
Sail out to sea and do new things.
-"Amazing Grace" Hopper

Avatar image of me done by Chidori.