I use ed frequently for writing quick scripts. Its edge is that you can use it while retaining visual history of the prompt.

Though, you could instead just redirect cat to a file and then do any tidy-up in your usual editor.

It's also sometimes useful when you're in a remote system that is behaving strangely due to screwed-up terminal definitions or some other catastrophe.

I'd be interested to read a sam tutorial focussed on using just the console version of the tool (i.e. not using the windowing system). I understand it takes a lot of ed's features and beefs them up.