Probably just that you don't want one narrator to get a huge chunk of the plot and the other to have a minisclue part of it. Or at least that's what I got out of it.
What I would recommend is to make sure your two PO Vs
are distinct enough to be differentiated. You'll probably just state which person's POV it is at the beginning of the chapter, but some readers are dumb and won't be able to tell the difference.
EDIT: I am not a particularly huge fan of shifting PO Vs
myself, but it can be done. Some of the Animorphs books (the Megamorphs, I believe) have multiple PO Vs
; you could always look at them to get some sort of idea how to do it.
edited 28th Mar '11 2:07:56 PM by Arctimon