I had a graphing calculator for high school maths in the UK in the early 1990s. For me the main use case turned out to be "much better user interface than a plain old calculator" -- you got a screen that was big enough to show you what you were typing as you went along plus some of the previous things you'd calculated, plus a backspace button. Plus at the time it was a neat geeky toy that I could persuade my parents to buy for me :-) I wrote a few little programs in the not-very-powerful-or-flexible script language it used, and I probably did a little drawing of graphs just because it was there, but just having the bigger screen was the killer feature.