What are the advantages / disadvantages of each location? In my picture below I have a breakpoint view and I can put a custom property at location A and location B however I can't tell if there is a fundamental difference in these locations? Any thoughts are appreciated.
Sorry I don't have insight on this, I've wondered the same thing myself.
Upvote on input on this one.
There's no real performance or other implication to either. Any child component is able to access properties on the view via a shortcut, so it's a little bit faster to type, so that might give it a slight edge.
To add the mess you are forced to put message handlers on root so I am inclined to believe I should also put my custom properties on root so when I send variables around the app the message handler and custom property are at the same location.
Thank you for clarifying.
One day, maybe in v9 
, it would be nice to have parameters, properties, and message handlers in the same location.