Sorry for all the questions lately, I'm trying to learn Poser and come up with new questions on a daily basis, most of them google can help with but not all ;)

Anyway, I'm trying to figure out IDL and am a bit confused. 

Is it mainly used for "outside" setting renders? I have seen some IDL light sets being sold that feature a sphere that iluminates the scene and such...is this mainly for outdoor settings renders?

What If I'm mostly doing portrait shots and indoor shots? is enabling IDL still going to give me better results? Do I need to use the sphere and such for portraitsindoors renders or should I just enable IDL and use my regular lights? (3 point lights, etc)

Is the improvement in indoorportrait renders going to be significant enough to be worth the render time increase?

Any other info you can share on IDL in general would help a lot, thanks! :)