I use an app on my phone and tablet for keeping all my vehicle data in a common place. They sync between each other. Fuelio has the option to back up to Google drive or Dropbox. I use Google drive for my backups. If I lose my phone, I have the tablet. And the Google drive backup.
The app has auto backup, so I don't have to do it myself. It syncs between devices too.
In answer to your question, yes, I had to use my backup a couple times. Something went sideways and my data on the app got messed up.
I selected Restore from Backup and was up and running again. Easy.
If you choose a spreadsheet and manual entry, backup is as easy as dropping the file on a flash drive - done.
I keep a paper log book in my truck. All entries get written there as they occur, fuel, maintenance etc. The book resides in the cubby in front of the console. Every couple weeks I take my paper log book and update the app.
In the event of a total digital loss, I still have the paper log book to recreate it.
In the event of a log book loss I have the digital copy on the app. It will export to .csv. Open the file, print it off to have another paper copy if I want. I have all receipts of every dime I have ever spent on the truck.
My log record is used at tax time, as it is my work truck. Accuracy counts. It will give me reports of totals in the various categories. I copy those to my tax filing info for my accountant. If audited, I have all receipts filed and a money management software program to track it all. I also have all truck expenses recorded in my money program, and can run reports from there.
I figure I have covered all bases.