Originally Posted by Will C.
Now, the other day I was talking to an old tailor and FINALLY, I was given an argument that actually makes sense.
To understand this reason, you first need to understand how woven cottons stretch. If you have a dress shirt made from 100% cotton (most dress shirt fabric), you'll notice that the fabric has threads running both vertically (warp) and horizontally (weft). For most high quality woven cottons, the fabric will not stretch very much at all if you try to stretch it vertically, or if you try to stretch it horizontally. However, if you try to stretch it diagonally it stretches pretty easily. (Go ahead - I can wait...)
So, the real benefit of the split yoke is that by rotating the fabrics to the angled orientation, we are basically adding stretch to the yoke across it's width! I can see how this could make a real difference in comfort. When you're tying your shoes, or driving a car, or lots of other every day activities, you put pressure on the yoke and if it is a split yoke it will stretch to accommodate your movement better. You learn something every day.
It's a good point, but even that doesn't make a great deal of sense, at least nowadays.
Looking at shirts of mind that have split yokes, most of them have not orientated the fabric diagonally - it is still horizontal. In fact, I think that the only shirts of mine with split yokes that have diagonally-oriented fabric are my bespoke H&K shirts. All the others are oriented horizontally.
Therefore, I would have to conclude that nowadays, split yokes are by and large simply a cosmetic feature, rather than a practical feature on most shirts.
I also think that the most-often cited reason, that of "fit" - that is, the idea that having a split yoke allows for a more precise fit - doesn't make a great deal of sense.
If you are making a shirt for someone, why not just cut one side of the yoke longer than the other if you need to make it fit? It doesn't require a split yoke to have one side of the yoke longer than the other.