What will this option do?
By default, pages that are restricted will still be visible in the page menu regardless of whether the visitor can actually access those pages or not.
If you'd rather display only the pages that the visitor has the ability to access, there is a setting you can enable to hide pages that person cannot access.
What this means for non-registered members
While this setting can help reduce confusion by preventing visitors from trying to view pages they cannot access, if most of your pages are restricted for only registered members to view, it could discourage members that do not have an account yet from registering.
This is because when viewing your website, they wouldn't be viewing it from a registered account, and therefore, wouldn't see all of the pages that would be available once they are a registered member. They may not feel a need to register, since they wouldn't know they were missing out on accessing information.
A note on folders
When you have chosen to hide restricted pages and a folder contains only pages that are restricted from the member that is logged in, that particular member will not see the folder or the restricted pages within that folder.
How to hide restricted pages
Visit the "Settings" section in the Admin Control Panel and click on the tab labeled "Miscellaneous."
Remain on the "Hide items" tab.
Check the box next to the "Hide pages in the menu that visitors do not have enough privileges to view" option.
Lastly, click "Save."