Can you explain how posting to sub boards and parent boards allows users to view hoots.

Sub-boards are a great way to enable corporate to push down communications/management to push content to different sites/departments. 

For internally facing boards, only Admins can rehoot posts to push them down to any sub-boards. This also allows you to share information across sites.
For public boards, a post can be rehooted to a sub-board or any other board on HootBoard since the hoot is public.