Of all the potential losses that can occur in the event of a computer failure, the loss of the contents of your hard disks is the most problematic. For a price, everything else can be replaced. Your data cannot.

What you hold on your hard disks is what distinguishes your computer from another computer of the same specification. When your computer fails the hardware is replaceable with new hardware of the same or better specification. The same applies to the sofware. What will be missing will be the rest.

For the home user this may be their irreplaceable photgraph collection or their music collection or whatever else the computer was being used for. If it has not been backed up it may be literally irreplaceable.

A business may not be able to run without its data and have to cease trading.

Data backup can help to protect you from data loss from hardware failure. It can also protect you from data loss due to human error in mistakenly deleting files later found to be wanted.

Data backup strategy needs to be planned taking into consideration the amount of space for keeping backups, the rate of change of the data and the acceptable recoverary timescales.

Consideration also needs to be given as to where the backups are kept. I have heard of businesses who have kept their backups in the safe, relying on it being a "fire" safe only to find that the safe is designed to protect paper and their backups have been rendered unusable by heat because paper has different characteristics and survival requirements from backup media. Where required, I can offer offsite storage for backup files.