So we learnt about how Cornerhounds are not actually separate beings, but the same will in multiple bodies/avatars.
I suspect most beings that are much the same, both Outsiders and regular spirit creatures. But the more mortal they have in them, the more independent they are from the Source. Hence why I think White Court vampires are more free than other vampires, more able to act. Whereas Black Court are really just another being spreading it's will through multiple corpses. The Reds are somewhere inbetween. The whole thing about the power of the blood being spread thin.
It therefore makes sense that Angels are likely in the same boat...they are extensions of TWG. But I suspect there is a slightly different deal. Because I think mortal souls are somehow connected, and because TWG has clearly some level of Free Will (although the whole "more power you have less flexible you are" type thing still applies), I think this is why Angels can sort-of Choose. I also suspect Christ (and perhaps other beings/persons) fit into this model - they are avatars of the greater being. I also suspect the way lots of beings get around not being able to affect events in the mortal world is by having various lower levels of themselves interact.
This isn't new stuff really if you have been on the boards a while. Serack's GUMCT says a lot of similar stuff, as do a few others.
But my WAG is that Harry is being set up to do something similar.
Harry projects himself at one point into an ectoplasmic shell (just like the being behind the Cornerhounds). Harry would need a LOT more energy and perhaps a different (read: freed) mind in order to do multiple avatars.
But I think he'll be doing more of this stuff by the end.
Come to think of it - who knows how many other Wizards haven't done the same? Cowl? Kemmler? Who knows?