How does the Particle Instance modifier work? I'm trying to figure out the Particle Instance modifier and how it functions, but as yet have had little success. I'd greatly appreciate it if somebody could give me a rundown on its functions and how to use it.
This modifier allows FX but works only with another object that has a particle system.
An example:


Add a cube and give it a particle system with Hair,
Add a UV sphere and apply particle instance to it,
Now, in Particle Instance, select the  cube in the object field.
In Particle System experiment with hair length.


Try out all options.