Restoring an entire user from an external drive when the internal HD fails.
Speaking of drives and HDs, they are most often still a Hard Disk Drive (HDD) and offer slow speeds compared to SSDs.
Firewire 800 would be enough for that, USB 3.0 would be overkill and Thunderbolt would be just a waste for this.
Fast platter based HDDs offer 100 MB/s and a bit more, current SSDs offer 450 to 600 MB/s, but almost no one uses an SSD as backup device, as the GB/price ratio is still to high to make it a valid choice for such a task.
Only if someone uses the fastest SSD to backup to and also the fastest SSD as internal drive, from which one backups, Thunderbolt can at least be satisfied of being used at half its potential.
Or one uses a striped RAID box to backup to, though not really a good choice to backup to, unless the striped RAID is mirrored again, to get even half the speeds TB offers.
In other words, TB is not really that slow to offer advantages over USB 3.0 or Firewire 00, to use it as backup tool.
But then again, those are just numbers, hell I do not even have a 2011 or 2012 Mac, so I am still using "old" technology.