Since you cannot place them anywhere else besides locally, why then not automatically deploy them there?
When you have many, it obscures the map. One one hand, it's nice to know what you have, but it would be faster to click auto deploy.

I like your reasoning.

1) There is autopilot; you are a member, so you can use that.
2) Bonuses can consist of multiple territories, how would warzone decide where to place those armies for you?

Auto pilot does not auto distribute local deployments.

Ooh, it doesn't? Always thought it did. How does the AI make a turn advance in a singleplayer game then if Local Deployments are turned on.

I am mistaken. AP does deploy them. But not strategically. Besides, Autopilot AI is weak and has limited capabilities, therefore is of no use.

As for the second part of your ^ reply,

How does the AI make a turn advance in a singleplayer game then if Local Deployments are turned on.

I do not know.