"IDL emitter" is a misleading label for the box;  it might better be labeled "IDL enable" or something.  It actually just means that the item participates -be it actively or passively- in IDL calculations.  A glowy prop would be an active IDL emitter;  skin would be a passive diffuse/specular/SSS reflector.

     Hair is especially IDL resource-intensive because it has multiple overlapping layers of transparency.  So, you could expect that traditional transmapped-plane foliage of a tree or bush will also  bog you down.  That's why I've switched to mostly making mesh foliage.  I wish there were a way to substitute two arbitrary meshes in place of the two transmapped planes ("leaf_adult" and "leaf_young") for Ivy Generator.  :)  Actually, I would like a third mesh added for things like blossoms or fruit.  That would be bodacious.

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5