When you uncheck "Light Emitter", every ray of light that hits that surface.. stops there. It does not pass "Go", it does not collect 200 more bounces...

That might not matter at all in some renders. Hair, especially, is problematic as, IIRC, IDL and transmaps have problems sometimes in Poser and strip hair, or any hair, by its nature has a bajillion different faces/verts/surface point to bounce light off of. Besides, it's not likely you're going to care very much about losing those bounces.

Unchecking Light Emitter for an entire posed figure may not be an issue, either. Especially if its clothed.. But, for any figure, clothing or object that is the primary object in the scene and receiving the most direct light, unchecking Light Emitter might rob the IDL of the rays needed to give a realistic render.

I'm no lighting wiz nor IDL guru, I just started trying to learn this stuff recently. But, I would uncheck Light Emitter from everything except the focus object, if it's large in the camera, and the bounding objects or environmental object I'm counting on to bounce the light around in the scene. Everything else gets unchecked. I don't need poser calc'ing light bounces off a potted plant when I have fifty-eleven large surfaces that are ready, willing and able to bounce the lights around for me...

 

PS - I'm talking directly from ignorance, here. So, if I'm wrong, I will refund everyone the money they paid me to read my opinion... :D