This is a really important matter when it comes to your photography. We all have those moments when I our primary camera body goes down and has to be sent in. In the perfect world it happens right after a trip causing no discomfort. Unfortunately it usually happens right while your doing something. That’s why it is so crucial to have a good backup body. I see and hear a lot of photographers go out and spend money on new bodies and more and more lenses. But they don’t always put the money back into a second body.
If you think about why wouldn’t you? If your going to spend the money on the latest and greatest why would the backup be something so much older. I’m not saying carrying two D5’s or two D500’s is the way to go but have something that you know will do a quality job if something does happen. For myself, right now my backup is the D4. I’ve shot with it for years, I know how to use it and I’m comfortable with it. It will still do a good job regardless of when it came out. But that’s just me. If you’re thinking about upgrading keep in mind that you also have to upgrade that backup body.