The slider serves as a simple privacy reminder on your home page. It only takes a few moments at youropenbook.org to make it clear that many people could benefit from such a reminder.

It's not the intention that you would interact with the slider frequently. If you drag it to a different setting a dialog box would popup and explain exactly what the consequences would be.

Most people would be happy with simple privacy settings, and there's still a customize link for the power user.