It does what is says. Adds an option to limit custom post types to certain users roles.
Found this plugin after several hours of struggling with 'members' and 'user role editor' plugins. (both of which I couldn't get to work).
A word of warning, this plugin (same as members and user role editor) do not allow to remove edited roles. So, use with care and save yourself a database trip (wp_options > wp_user_roles).