Even if a profile is private, some photos might remain public, or the user may be tagged in public photos.
: Occasionally, photos indexed by search engines before privacy settings were updated may appear in Google Images. Searching site:facebook.com "User Name" can sometimes reveal these. Risks of Third-Party "Viewers"
This feature is a one-click solution to dramatically increase your privacy. When you lock your profile, only your friends can see your photos, posts, and stories. It also changes all your past public posts to "Friends only".