Okay, think I got it:
Gallery config guest is one-only; share with everybody to have multiple. No rights, login/no logout. Sees only published albums only. Look-only, can't do nothing.
Admin info guests can be shared OR create one per person but is ALWAYS given restricted access to their account details (minimum). Can change their info (if they know to click the Admin Toolbox menu). Thereby blocking sharing the account with others if they change password. Can see invisbile images (???). Can see ALL (published/unpublished) albums.
So, if like your reply to the other poster, you want to share an album with "special" pics, that guest also gets to see unpublished/in progess albums too.
Well, not quite. Gallery users have to login. And with judicious use of the user_logout plugin they can also log out.
Only Admin users see the 'special' pics (The unpublished albums and not visible images.) Gallery config guests do not see these.
Otherwise you have it exactly correct.
And with judicious use of the user_logout plugin they can also log out. svn1808 (just doing last night's after this post) --- why "judicious use"?
LOGOUT: From Gallery Config, logout opt enabled, I don't get the Admin/Logout anymore. Probably better because then there's no Admin for them to get to and change profile
User logout: the link for user info goes to the Testimonial page about ZP on the Plugins page