What this mod does is interesting, to say the least. I've never seen something like this before, the concept behind it though is rather simple.
For example, you can have an account on your forums named "Admin", and have that as your sole administrator while you, yourself, use a regular member account and participate in your community as normal. Now, when members send PMs to the "admin" account, instead of sending them to you or instead of you having to login as that admin account to read them, all those PMs are posted in a private staff board that only you and trusted people that you allow can view them. When a reply is made in the topic, a response PM is sent back, but as "admin". It allows communication as staff through the private message system.
If anything, it gives you more privacy.