There was a time that ed was necessary knowledge because you often had richer editors installed on a different partition from the boot partition and more freque

There was a time that ed was necessary knowledge because you often had richer editors installed on a different partition from the boot partition and more frequently than you would expect you ended up in a position where you were only able to bring up the boot partition or had to boot emergency media, both of which only had ed. That wasn’t a preference thing, it was a necessity thing. Trying to learn how to use ed when production is down (and you might not have a readily available command window with man pages available when you’re in a data center on a vt220 plugged into the dead system!)