Week 10 Application Settings
An example of preferences that might change frequently include things like the volume levels or control options of a game. An example of preferences that might change infrequently are the email address and server settings in the Mail app. For iOS apps, it is ultimately up to you to decide whether it is appropriate to expose preferences from the Settings app or from inside your app.
Chapter 9: https://www.dropbox.com/s/phtvlpkow5o0n9r/IOSBOOK.pdf (Page 231 PDF)