My big fear is losing all my data in some sort of system crash. Well, I just had a system crash last week (bad hard drive). As it turned out, it was marginally painful. My backup system was designed for managing my data. Fortunately, my data were on the drive that survived. The dead drive housed the system OS.
After some false starts, I managed to find an old copy of the system and restored it onto a new disk. Within a few hours, the system was back up to normal, more or less.
Although I didn't backup as religiously as I should have, even a marginal backup scheme prevented a total loss. Any backup is better than none.