I used this last night to install High Sierra on an old MacBook Air. I wish it didn’t require a Terminal command, though. Why can’t the macOS installer apps include an option to create a bootable installer? Seems like that could come in handy.
But I did hit a road block along the way. My MacBook Pro has Catalina installed and I wasn’t able to download High Sierra from the App Store — it just kept throwing an error. I ended up downloading it on my Mac Mini, which is still on a High Sierra. But what would someone do if they didn’t have access to another machine with an older version of macOS installed?