From QAbstractSlider:
If tracking is enabled (the default), the slider emits the valueChanged() signal while the slider is being dragged. If tracking is disabled, the slider emits the valueChanged() signal only when the user releases the slider.
and here:
This signal is emitted even when tracking is turned off.
I assume setValue() will honour the tracking behaviour, and setSliderPosition() will always announce changes through sliderMoved() even when tracking is off.