Did I ever learn about this the hard way. About a month ago, my hard drive died. My laptop had been giving me enough warning that something was wrong, but I ignored the signals. So one day, I couldn't get rid of one screen that made absolutely no sense to me. I took it to a computer repair place and found out it was the hard drive. The guy replaced it to the tune of $99.99, and the rest was labor for a total of $226.99.
I lost everything but my emails for both of the addresses I have and the address books for both. But all of my pictures are gone. Fortunately, I do still have some on two memory cards, so I can put some back on at some point. But it will be a pain to figure out just when they were taken. I lost all of my recipes, everything in My Documents, some family information, and a story about my son's life, who died 16 years ago.
The place gave me the name of a place that may be able to recover the information. I just haven't taken the time to call them. I know it will be expensive.
Back up the things you do not want to lose. The place where I took my laptop, tried to recover at least some of the things, but they were unable to do it. :(