Great topic. I have thought about this quite a bit. It is very strange to see two holes that run parallel to one another, traverse similar land, and play similarly. I believe Ross did this more than any other respected architect. Here are a few examples:
1 and 10 and Inverness: We've already discussed this one. Yes the greens are different, but the tee shots feel almost identical, and with only short-iron approaches, the two holes seem to play very similarly.
5 and 9 (I think) at Peninsula G&CC in California: They're almost identical ~450-yard par 4s, the terrain is very similar, they're right next to each other, and they feel very similar to one another.
1 and 4 at Carter CC in New Hampshire: These might be the clearest example I've seen. The hole lengths are exactly the same, and both holes play up the exact same ridge to similar greens. This one seems especially odd because it's only a 9 hole course. The ridge is really cool, so you'd think it could have been used in a slightly different way on one of the holes.
1 and 10 at Skokie CC in Illinois: These two holes are different from one another, and 1 does play longer. But both nines at Skokie start with par 4s that start in the same place and head in the same direction down the same hill.
I can hardly think of an example like this for another respected architect, and here are at least 4 examples for Ross (and there may be more that I haven't seen or don't remember). I've wondered why he would do this. One explanation is that he was phoning it in (maybe he thought the shot up the big ridge at Carter was so fun that he'd have players do it twice in 9 holes). Another explanation is that he thought that by doing this, he could get more variety in the other holes. Few of us enjoy playing a boring routing that just goes back and forth. So maybe Ross thought a good solution was to play two similar, parallel holes and then branch out from there in different directions. But it's interesting that MacKenzie, Maxwell, Flynn, Colt, and Tillinghast had many brilliant routings and rarely (never?) had to do this.
Perhaps the strangest routing that I am aware of in this regard is Exmoor CC in Illinois. Exmoor arguably has 5(!) pairs of sister holes. That is, more often than not, you're playing a hole that has a sister hole on the other nine. The pairs are 1 and 10; 2 and 11; 4 and 13; 5 and 14; 6 and 15; and 7 and 16. Yes, the sister holes are often different lengths, and in two cases, the pars are different. But in every case, the holes are next to each other, run in parallel, play over similar terrain, and often play similarly. Strangely, the routing works well, and there is plenty of variety. But if you were re-routing the course from scratch, you probably wouldn't want so many holes that are similar to a hole on the other nine. (Potentially interesting aside: Exmoor calls itself a Ross course because Ross made some changes and recommendations in the 1910s. But Stewart Gardner is responsible for most of Exmoor's routing, so Ross gets a pass on this one. Although I wonder whether another architect would have recommended more changes to the routing. Ross apparently didn't mind the parallel holes, so he left it more or less as is.)