Recommended: Encrypt Your iPhone Backups!
Why it is recommended, maybe you are asking. Encrypting your iPhone the same time when backing up with iTunes you will enjoy two positive things, increase the security of your data, and make restoring more convenient.
Also, do you know that iPhone keeps record of everywhere you go? I bet you didn’t know that.
Let me quote you a paragraph from Marco Arment, letting you know why you should encrypt your iPhone backups:
You should encrypt your backups, if not for security reasons, for a big convenience gain: encrypted backups will include your email and Mobile Me passwords so you never need to re-enter them after a restore. (emphasis added)
Find the specific checkbox on your iTunes summary screen. You can see the exact picture above, if you really don’t understand what I am talking of. Now you know why the title is starting with “Recommended”, keep this in mind, is for your safety.