I found this out the hard way (is there any other way?)
I 'assumed' versions would work like 'autosave' under Windows (at least the last time I used Windows, several OS's ago) and that even before I titled a document it would be saving the 'untitled' document. Ahem... nope.
I was working on a project and had to quit Pages and I thought "How cool, I can just close the app and when I reopen it my article will still be there. That did not happen.
Lesson learned but after waiting years for a simple autosave this seemed like an oversite. Okay, it was user error, but still it hurt like a son-of-a-bike!
And I'm really vigilant about backing up too. I have Time Machine going, I back up almost daily to a thumb drive, I have a symbolic link to my documents folder in DropBox, but none of that saved me at the time. Time machine would have I suppose but it hadn't run since I started writing the article.
For a lot of stuff I use a 1940's Remington Model 5 typewriter, and what's amazing is that when I'm done there is magically a pile of paper beside me with everything already printed out in hard copy. Ikr?