I was taught in college that, as a professional, if you don't have 5 copies of your file you don't have any. Backup backup backup!
Not quite in college - that was 50 years ago - but since then I taught my students in college something much the same. As important as how many you make, though, is where they are. Keep a copy off-site. Maybe one in the car etc. And especially not all connected to the same PC at the same time. But you knew that.