What are Sets in the particle tools??

Hi guys
I had some confusion in what "sets" mean in the particle tools?
i recently read in the book "the vfx fundamental: Fusion 8"
that it is best to use the pspawn in set 2
does the pspawn doesn't work if is not in a checked set??
please let me know if i am wrong??
please and thank you
I had some confusion in what "sets" mean in the particle tools?
i recently read in the book "the vfx fundamental: Fusion 8"
that it is best to use the pspawn in set 2
does the pspawn doesn't work if is not in a checked set??
please let me know if i am wrong??
please and thank you