... and then carrying that scale around like you do a phone? Lots of things are being replaced by phones/apps because you always have your phone. Do you always have your scale?
While I personally can't recall a time when a scale-in-my-pocket would have measurably improved my life, I will concede that often capability leads utility. Maybe a future where everyone's phones are also reliable scales will fulfill needs we didn't know we had.
No I have no need to carry around a scale at all times. But I do have a need to carry around a working phone with a screen that isn't scratched, broken and with a force touch sensor intact.
Again if you are the sort of person that is willing to risk a $700 phone because of the inconvenience of carrying a scale then I suspect you may be a niche consumer for Apple.