Yesterday I had the "pleasure" of wiping and updating my phone under the assumption that my app backups worked. Imagine my surprise when I booted my phone and saw that Titanium Backup wouldn't restore from backups because they were corrupted! To say I was disappointed would be the understatement of the year! I lost so many things: screenshots, app data, app backups, etc... The only thing I didn't lose were my camera photos, which were thankfully stored on my SD card. All that said, let me first say that the main lesson here is to backup locally and then backup to another location when performing potentially dangerous tasks.
Before updating, I went through the painstaking process of backing up each and every Line conversation I had. As you may know, Line is a battery-hogging chat app that doesn't support multiple devices well, nor does it keep any significant chat history between devices. So I manually backed up all my conversations. On internal storage.