Especially if Pages suddenly quits working.
And you lose two hours of work.
But, you tell yourself, you just did those two hours of work, so it's not so bad. You can recreate them much faster.
And then you realize that the editorial letter you have been making comments on for TWO FRICKING WEEKS is also gone. The one that had all your reasons and explanations for the changes you made, written as you made them. The one you never actually, um, saved. So there isn't even a backup of any sort.
I found this shareware - if you are in a similar situation, you might want to download it. I set it to back up every five minutes.