When the US 4x100m swim relay beat France about three olympics ago (the one where Phelps won all those medals), France was comprehensively faster man-for-man aside from Phelps in that relay.
The US won because Jason Lezak, the anchor, swam in the wake of the final French swimmer (a draft basically) and was able to save energy and pass him.
If the US and French had been separated by a lane, the US would have lost.
If you are slightly faster (and especially if you go out faster) than your #2 rival, you want to have a lap between you to deny them the draft.
https://www.youtube.com/watch?v=kQNY5htc9_k
When the US 4x100m swim relay beat France about three olympics ago (the one where Phelps won all those medals), France was comprehensively faster man-for-man aside from Phelps in that relay.
The US won because Jason Lezak, the anchor, swam in the wake of the final French swimmer (a draft basically) and was able to save energy and pass him.
If the US and French had been separated by a lane, the US would have lost.
If you are slightly faster (and especially if you go out faster) than your #2 rival, you want to have a lap between you to deny them the draft.