As with all computer systems, your work on the i5 should be backed up periodically so that you can recover lost data. Losing data is disastrous if you don't have a backup of everything you could possibly lose. It is better to be safe than sorry. Data can be lost for any of the following reasons:
Someone accidentally deletes an item such as a file, a program, or a library.
Someone intentionally and maliciously deletes an item. Pressing charges for sabotage and suing the person will not bring back the missing item.
The mass update program you created did not work as expected, so your database is mangled.
The new Accounting clerk selected the wrong menu option, ignored all the warning panels with bells and whistles you designed to make the clerk stop, and closed the fiscal year instead of the current month. The clerk will be fired for gross negligence, but you still have to restore the general ledger.
One of your disk drives went down, and you will have to replace it. The manufacturer's warranty will get you a free replacement, but everything the old drive contained is irretrievable.