If you own a computer/laptop you will know how important your hard-disk. You keep your work, assignment, music, movie, image etc in your hard-drive or hard-disk.
Because you don't know when your current hard-disk will be a problem. It happen to me but luckily I have an extra hard-disk.
If you are a heavy downloader, consider extra hard-disk for your own good. Even you have a great anti-virus but still be cautious is better for your computer's health.
p/s: Beware of the virus!