That's not just Mac OS and professional software either. Windows did that too. I was very young back then, but I do remember being angry at the computer crashing and losing whatever I was doing, only to be told "it's your fault, you should save you file more often next time". It becomes a sort of a subconscious habit really quickly.
The important point being, once you saved, the working memory was also reset to sane conditions and you could keep on going for days, or weeks. Saving frequently not only kept the injuries, which added to the insults of a crash, in bounds, it also prevented those crashes from happening at all.
