Have you ever had a program quit and realized you had not saved your file yet, had the power go out or your computer crash and lost hours of work? It only takes that happening once or twice for me to become vigilant about saving. On a grander scale, have you ever had a hard drive or back-up drive fail, a laptop stolen? I've heard too many stories of these things happening and friends losing years of work files or personal photos.
For many years now I've had a pretty inexpensive system of file back-up in place. All of my files live on my computer's hard drive (copy #1). Any project in process is backed up onto an external drive every day when I'm finished working (copy #2). Once projects are completed they are set aside to be archived. When work is slow, like now, I burn files ready for archive onto CDs or DVDs. I make one set that is kept here in my office (copy #3) and another that is sent to live on a shelf at my husband's office at work (copy #4). Should the worst case ever happen and my house burns down, I would have a copy of all my files safe and sound.
A little van Gogh livens up the cover and a burn date helps me find files later. Inside is a listing of the contents of the disk to further help in finding that certain file years later.