There’s a couple things… First, it’s a habit to be constantly pressing CTRL+S. I’ve been doing it for many years, I’ll continue to do it probably until I stop using a keyboard. It’s such an easy keystroke, since my hands are almost always hovering over the keyboard. Second, in some software you can create new documents without first creating a file on disk. This means that when I go to hit CTRL+S, it prompts me to save the file. That’s not to say that some software can’t save a recovery version of the document in the event the software crashes, but I’m not going to bet money on it working 100% of the time. I’d rather be proactive and personally make sure my work is saved. Gives me peace of mind.