It depends, really. The staff section obviously must be hidden, in my opinion, as you wouldn't like guests to see how the site staffs run around and manage things to keep the site alive, right? Also because usually staff section has important and sensitive messages.
As for non-staff sections to be hidden, it depends. I mostly agree that hiding something from guests is not a good idea. However you may have sections in which members post something personal there, like a journal entry or a design or whatever it is which would require the site to protect it from being 'stolen' or simply to respect the privacy of the authors. I have that section in my site, thus hidden, as requested by the members as well.
As for non-staff sections to be hidden, it depends. I mostly agree that hiding something from guests is not a good idea. However you may have sections in which members post something personal there, like a journal entry or a design or whatever it is which would require the site to protect it from being 'stolen' or simply to respect the privacy of the authors. I have that section in my site, thus hidden, as requested by the members as well.
