It's not superior, it's just a different type of data.

With Fitbit you also get heart rate, active times (gym, sports), combined with the optional phone-enabled location you can know person X goes to gym Y twicer per week and spends 1 hour doing HIIT. You can also get data such as sleeping hours, sleep patterns, at what floor a person lives or works (if he climbs the stairs).

You can't see how an advertiser might like to know how your heart rate, say, is affected by a particular advertisement?