I've kept getting notifications on my iPhone & iPad because I'm out of space (I'm on the 5GB free tier, no way I'm paying for cloud storage when self-hosting isn't hard). I still keep app data backups on, but despite that the device backup sizes would be ~1.5GB large. God knows what's inside the backup, while Apple does have a list of what's inside backups, you can't see the contents of your backups without restoring. If either of my devices were lost / wiped, I would lose no data either than settings or home screen layout, since all my app data online, either iCloud or on an online account (I just checked both of them).