Q: Do I need a backup for the updates iOS 9.34

You should always take a backup before updating the OS on any device or computer, they don't always go smoothly

I would definitely back up mine before updating.

You only need it if something goes wrong...that said, once something goes wrong it's too late to wish you had made a backup.

I ALWAYS backup before I update. Murphy's law, if you have it it increases the chance of not needing it.