It's from a bygone era. An era when you'd lose hours of work if you didn't go file -> save, (or ctrl-s, if you were obsessive). If you reboot, you lose all of your work, your configuration, that you haven't saved to disk. Computers were scarce, back in those days. There was one in the house, in the den, for the family. These days, I've got a dozen of them and everything autosaves. But so that's where that comes from.