Quote - i never got why would you buy light sets. your scene is set up by you so you and only you know how to set up the lights.

well, that's how i feel.  but i will say the exception is the same as the one where i might need lots of lights.  if you have a prop or scene with a significant number of light sources, and in Poser there's no way to make illuminating materials... well, you might turn to someone else to create the effect of, say, the lights going down Stonemason's Skyline hallway or his GSFC.  long ago, i tried to light the latter with points, and really i should have tried about 4 or more point lights with particular settings to duplicate their effect.  now, i might try this IBL tool, but i'm not sure Poser's IBL is that precise.