Data loss can be a real nightmare for people who make a living off of their photos. If a writer loses a story he just wrote, maybe he misses a deadline. A photographer has to deal with missed deadlines, as well as the cost and humiliation of bringing models back. You can't guarantee capturing the same magic you did the first time around. Freezing moments of life in time, and putting them on disk, is the kind of task that relies on your equipment working the first time.