QTR-Quadtone RIP

I posted this on the B/W group and received no repsonse, though someone helpfully 
directed me here. I hope this question doesn't seem too "first grade":

I use a 2200 with Mac OS X, using K2/Eboni with either BO or QTR (with which I am a 
complete beginner). I've read a few threads where people mention using the ink limit 
adjustment with certain papers...how do you know which papers benefit and by how much 
to pull back or add? I use mostly EEM/HPR.

I guess what I'm saying is I don't really understand the tool. Is there someplace I can read 
about it someone could direct me to? I have read Roy Harrington's .pdf for QTR and am 
still unsure when or why to use this.
 
Thanks for any clarification someone might offer!
Sarah