Back in the days before computers I knew of practices that were destoyed by fire or flood and lost all their records. In those times there was no practical way to back up all the paper files, so the catastrophe victims just started over from new blank records.
Office business insurance ususally had a benefit for this eventuality.
It's probably more common to lose a server through random error, vandalism, accident, etc -- but those things seem to be amazingly tough, and it doesn't happen very often in small practices so far as I know.
Backups seem to be relatively easy. However there appear to be a number of ways to do it. I wonder about the corporate environment -- seems like data loss can take a major corporation several days or longer to get straight. James mentioned something about a "test server" Does AC allow us to have a backup "test" server? I never asked them.