I have noticed that when I take my Apple Watch off and walk around with my iPhone in my pocket, the Activity app will sometimes give me exercise credit based on the steps/motion recorded solely by my iPhone. I have confirmed this by looking at the data within the Health app and seeing entries for exercise credit at time(s) that I was not wearing my watch. Also, sometimes when I rest my iPhone on the passenger seat while driving, bumpy roads will cause the iPhone to record steps and sometimes that coverts to exercise credit in the Activity app. On most days that I don't exercise, the Apple Watch has been giving me between 10-13 minutes of exercise credit (green ring in Activity app) based on normal movement/non-exercise activity. This morning I turned off fitness tracking on the iPhone (Settings > Privacy > Motion & Fitness) and have noticed that the exercise tracking on the Apple Watch is much more accurate. Today with fitness tracking on my iPhone turned off (thus making Apple Watch the only fitness tracking source), I was only given 1 minute of exercise credit - about right. Is there any downside to having fitness tracking on iPhone turned off if I'm always wearing my Apple Watch anyway?