however if significant advantage can be gained by amending the sequence, then it's valid to do it.
Or, avoiding an unreasonable penalty. VFR Cessna goes ahead of a 747 on departure because the Cessna can be turned out of the way before the 747 even gets into position. Nobody is delayed and you made the best use of the the runway and airspace. On the other hand, if they are both IFR on exactly the same route, the Cessna waits. Hence, the safe and expeditious movement of air traffic. Do the best you can for the folks so long as it's safe. Pretty pragmatic, actually.