I would have used something like this when I was first learning rsync...

Even though I had read all of the man pages and knew the commands inside and out, it still seemed incredibly risky and scary to me to run rsync with the --delete function when I was backing up my main USB drive for the very first time.

Basically my biggest fear was that I had source and destination mixed up, which I didn't, but it would have been nice to run a test trial of that command before doing so.