Why should you make backups? There are more reasons than you might think. Here are a few:
Typical computer surge protectors will protect you from ordinary power problems, but not big spikes like lightning strikes or the surges that sometimes happen when power returns after an outage.
These can happen without warning, no matter the age of the computer. In fact, a new computer is more at risk than a 2 year old computer because manufacturing defects may not cause a failure until the computer has been running long enough to burn out a marginal component.
You may accidentally delete an important file while doing housecleaning on your computer. All it takes is to click on the wrong file without noticing. Or what if you deleted what you intended to, only to later discover that you (or worse, your spouse!) needs it?
Many documents and data files are constantly updated. What if you need to review an old version, or maybe roll back to one?
Every time you install a new program or upgrade an existing one you risk a conflict of some kind with other software on your computer, or that it out-and-out won't work. The effects may confined to the new program, or it may cause your computer to crash unpredictably. In the extreme case it may disable your computer completely. Even if the problem is just an occasional lockup, what if you are modifying a critical file at that moment and the contents of the file are corrupted?
Are you the only person using your computer? Since you are reading this web page to evaluate backup software odds are the other people are less well trained and less sophisticated about using a computer than you are, and therefore more likely to make an expensive mistake.
Computer viruses and worms are an unfortunate fact of life. Good "computer hygiene" can greatly reduce your risk, but it requires conscious effort, diligence and good judgment. Considering the malicious nature of many viruses, you need to be prepared for the worst case.
If you think about these examples, you'll realize that while you can lower the odds there is no way to absolutely prevent these things from happening. And the more you use a computer the greater the odds because of the increased wear and tear and greater opportunity for human error.
The only real protection is to make regular backups: Backups you can trust to have what you need on them, and trust to be usable when you really need them.