Originally Posted By: tfabris
... the most important part of backing up is that the restore process needs to be reliable. Since iTunes backup and restore features are designed and tested by the people that made the phone, I feel like I can trust that one. ...
You must set a password specifically for iTunes backups. If the backup itself is not password protected then iTunes will exclude iPhone saved passwords and saved login type data from the backup.

And you must KNOW that iTunes backup password. The password is required to restore from the backup.

There is no ‘reset password’ feature, and once set the old password can not be changed unless you know it. Even if you connect the iPhone to a new computer, the old password remains in control.

A family member is in this position, and they cannot change the password nor use their iTunes backups. They just do not recall what password they originally chose. So they can ONLY use iCloud backup and restore. Been this way through a couple of iPhone upgrade cycles so far.