We need to build roads to settler locations. HOWEVER... We have to be careful on when the settler will arrive. i.e., we don't want to build a road, only to have the settler end up on that road during their last turn (that's several wasted turns.
i.e. (* = road, C = city spot, S = settler)
S*** **C
S*** **
(it's split so you can see it easier).
If we were to build 6 roads, to C, that settler will end up there, wasting the road. We'd need to build the road system the 2nd way (so the last turn ends up when the settler isn't on a road). That way, our workers can go to another area quicker.