I can personally attest to the importance of wearing ID. A number of years ago, my wife and I went for a training ride on a beautiful Colorado day. We were climbing Mt. Evans to build endurance at altitude. After I warmed up, I rode ahead by myself... and to this day I don't remember what happened next. Nobody saw me go down, so I'll never really know. My wife rode up to the scene of the accident just in time. The park rangers had already called in the paramedics. Soon after, I was headed to the hospital in the Flight for Life chopper.
Long story short, I had crashed on my bike going about 30 mph, and suffered from a TBI (Traumatic Brain Injury). I spent several weeks in the ICU, and five months at Craig Hospital for rehabilitation. At one point, my wife showed me the bag that had all of my cycling gear the chopper and ER staff had removed. The outside of the bag had "John Doe" written on it. I had ZERO ID on me at the time. I can only imagine what would have happened if my wife didn't arrive in time to see the accident.
Not carrying any ID is what I had always done and never thought twice about it. Now, my Road iD is the first thing I pick up before I start a ride, participate in a duathalon, go on a run, or when I am hunting in wilderness country. I'm happy to report that one year later, my wife and I successfully rode to the top of Mt. Evans together.