Yes, you're right about 'control-z'. On the Mac it's the Apple key (the one next to the space bar) and z. I use it a lot when I've made a simple mistake. My first problem with Time Machine happened when my very expensive Porsche hard disk, which I was using for the backups, failed. Died. Completely. (My husband has an identical disk and his is still working fine.) No big problem for me because I always make multiple backups of my files, so I didn't lose any work. Second time—a while later, after getting a new hard disk set up on my old 2012-era Mac Mini running Yosemite—it was the Time Machine itself that went wonky, and wouldn't allow me to make backups any more at all. On anything. I now have a new Mac, using Sierra, but haven't bothered setting Time Machine up. I have a clone of my system, and roughly 10 other backups in place. Two large, but portable hard disks that back up my major files—like my photos—in rotation. And the others are smaller flash drives that I use, again in rotation, two at a time, to back up daily work. One to keep at home, and one to carry on my keychain, etc. I'm pretty much covered. But I wouldn't trust Time Machine again. I do send occasional copies of things I can't afford to lose to myself as emails, which is a system I can access from anywhere. And I print off important documents as well. And I have a complete, up-to-date printout of my novel. And my novel's timeline, and a lot of the research materials as well. So I think I'm covered. Whenever I work on a file from the day before, I always make a duplicate of that file before I begin making changes to it. So I can instantly go back to the old version if I want it. And I keep a file of these old versions (in organised folders) for future reference. The only thing I can't do is go back and retrieve something I just wrote, if I've deleted it. If the Apple-Z command doesn't bring it back, I've lost it. That's where I need to be careful and keep my mind on what I'm doing. However, I don't put complete trust in any one thing. So far, so good. I've had to retrieve old work a few times in the past, but I've always had it to hand, in some form.