If you ever want to have public access to your dashboards you can get this by creating a guest user and giving that user access to the dashboards you want to be publicly available. This is great if you want to place dashboards on a web page without haveing the users to log in to see them.
You can create a guest user by creating a new user on the server with this info:
Now, remember that this user should only have access to dashboards that is intended for everyone to see. If you give it access to everything, business critical information can be available to anyone.