Nowadays, it does not seem all that important, after all, most people are getting away from even using pens, but in my school in the eighties, ink that could be erased seemed like magic. It was especially useful when you had a stickler for a teacher when it came to penmanship. Most of my teachers fell into that category and would force us to write our essays in pen. What made this difficult is that you were not allowed to cross anything out.