When will people learn to make good backups? It seems almost every week there's another story here about how people lost data because they didn't have backups.
Even when it is made easy and automatic, we still get folks asking us for help with recovering or repairing data that could easily be recovered from backups...if they actually kept backups. And, of course, secure off-site backups are almost unheard of (actually making backups secure from attackers that have root access is a pretty hard problem; or, at least, one that requires two machines).
Anyway, I've experienced it a few times in my career, and I can say with confidence that there are very few worse feelings than knowing a mistake you've made has caused someone major data loss.
Tarsnap handles this easily with restricted keyfiles. :-)