What will you do if you woke up tomorrow and found out that your entire digital music collection is GONE? What about all the photos and memories you have with family and friends - all gone? If you are like most people, you will proceed to the shit out of luck aisle because you did not backup your files. Good luck finding and downloading 10,000+ songs (legally of course... of course.) and trying to relive the precious moments in your live with only the memories in your head.
The digital revolution have pretty much consolidated all forms of media and files into one solitary machine (or two, if that is your cup of tea). Heck I am perhaps the perfect example. Of course my music is in digital form, immaculately catalog in the bloated software called iTunes. All my movies have been ripped into a digital format (h.264. mp4. ac3) for easy access and no disc swapping (I actually threw all the disc away - the minimalist in me). I grew up in an age of digital cameras, so all photographs I have are in digital form to begin with. With a scanner, any important document that I have is not locked up in a filing cabinet, but rather the encrypted space of my hard drive.
How nice is it to basically have everything in one computer? Very much so, plus it keeps my room clean because I have less things (paper somehow always tends to stack up and take up space like no other). Anyways, having everything in one object means that it is also easy to lose it when the object disappears or malfunction. Technology may be great, but the hard drive that stores all your digital files is still only a bunch of spinning magnetic platters read by a stylus (not unlike a LP record player). And as with anything that has moving mechanical parts, it can FAIL. There is a reason the most amount of years hard drives have warranty on them is only 5 years. They are NOT built to last, hence the data you have on it are not going to either.
Unless you perform backup. In essence, it is having another copy of your data on a separate device, or in some extreme cases, separate location (you'd still have a copy of your stuff even if your house burned down when it is stored at another location). For most people though, it means having another harddrive that stores the same information, and updating it regularly. Hard drives are so dirt cheap these day that there is really no excuse not to get some and backup your data (unless you are the type that likes to play Russian roulette).
And it is not physical deterioration of the hard drive you have to worry about. Computers in itself don't last forever (will save the conspiracy of windows for another day). Things from viruses to power surges can completely kill your machine. In that case all your data is gone too (well, not exactly, but do most people know how to extract data from a broken machine?). Another thing is, laptops are as popular as ever - so imagine a machine with all your stuff is actually MOBILE and prone to thieves (Starbucks laptop theft is at all time high I have read). In that case, perhaps losing all your music and memories may be the least of your worries.
There is another way to backup your files - online (to the cloud!). But unless you want to pay monthly fees, the amount of free space online backups give you (I use Dropbox, which gives on 2gb free - I use it only for my documents) is not nearly enough. Online is convenience in that you can download and restore anywhere there is an internet connection. The problem is the internet connection itself. Upload speeds are absurdly slow compared to download speed no matter what ISP you have, hence the initial backup of your file may take a long time. Even with the faster download speeds, downloading gigs of data during restore will still take much much longer than simply plugging in an external hard drive. Online store still have ways to mature for it to be truly mainstream (and the fact that people's data are increasing by the gigs does not help).
Nonetheless, the message is this - BACKUP your data. The cost is so cheap you don't have an excuse. Don't wait until that day comes when your computer goes kaput and all your files are gone. I sort of hate to always be a champion of Apple products, but if you have a mac and an external hard drive, there is software within the operating system that will do a backup for you automatically as a scheduled task (set it and forget it, thanks Rotisserie chicken machine). Even windows has its own backup software. But you don't need software, just drag and drop your files and you are good to go.
P.S. I love my music, so I actually have it in four places - the mac, external hd, iPod, and DVDs. Overkill? Not if I never lose it.