Props appeal to my "Keep It Simple, Stupid" mentality. Maybe it's because props don't occupy a multitude of lines that must be constantly collapsed in the hierarchy editor. (When will Poser allow you to collapse figures as a global preference?)

Anyway, I like to work with props whenever possible, even though I realize this imposes some limitations. Other people prefer to work with figures, even when they don't have to. Why does a simple chair with no moving parts, for example, need to be a resource-hogging and hierarchy-cluttering CR2? Because the creator makes CR2's out of habit, I imagine. I generally convert them to PZ2's at the first opportunity and stow them in the props folder.