As much as I know it depends on what clock are you talking about.
It would be a nice idea to calculate how many turns each barrel turn on a week and see if there is much difference. This is very common on quarter chime clocks – the quarter train runs almost the double turns than the strike train, so the spring will be longer.
Many german T&S clocks need more power to drive the strike train than to drive the motion train, so the strike mainspring will be thicker. If the spring is thicker, it will take more space inside the barrel and will be shorter to fit. In this case care is needed not to invert the barrels when reassembling the movement.