When parsing high end Garmin and Apple fit files, it appears a lot of their smoothing is done before writing to the fit file. They’re in a very workable state straight out of the gate.
Workout data might take it a step further, as you tell it the type of workout, and I'm assuming WorkoutKit might do something like adjust the distance filter that specifies how far the device has to travel before triggering a location update event to minimize battery use during the workout.