One possible use case is you run a CLI monitor app (stock, website traffic, etc.) and you need simple plots in it .

Debugging, mainly. And really really dirty and fast workflows, when you don't have time to do pretty graphics.

The other thing is not depending on GUIs, libraries, and stuff, makes it resilient and usable in hard conditions (e.g. if you accidentally remove some core system libraries but you still want to see a graph)

I use regularly UnicodePlots.jl for Julia when connected through ssh to HPC servers. It has boosted my productivity!

...always? Very often it's much cleaner to see your plots "inline" that on a separate window.