Before you get excited and add all your Unity subscribers, please take a moment to at least review the default subscriber template.
Other than maybe changing default passwords if you haven't thought about it during the install, you may notice interesting items in the call transfer section.
The default for all types (standard, closed, alternate) is "No (send directly to greeting)". Check the "Yes, ring extension for:" if you really need most mailboxes to transfer to lines. Then build them.