I have a number of lightweight jackets that I had made to measure while I was a customer of a Savile Row tailor for most of my clothes (the tailor in question was not Henry Poole, whose photo adds some visual interest to this post). You see, that was before globalization really took hold and these guys still believed they would never need to learn how to make jackets from anything lighter than ten ounce cloth (of course, they could have volunteered that there were ten ounce cloths that wore cooler than the worsteds they kept pushing at me, but that's another story).
What I consider the principal difference between those jackets and bespoke coats was brought home to me once again when someone at dandyism.com elected to run one of my photos in some kind of a contest on their web page (without photo credit, I might add,which irks a little because we internet publishers should be trying to support each other lest we hang separately). The armhole, or scye, of my MTM seersucker jacket is not cut very high under the arm, as more than one dandy reader pointed out.
Now big armholes like the ones on my jacket are good for the tailor and bad for the customer. It means the tailor can be sloppier - there's a story about how my first Row tailor increased the size of their armhole half an inch so they could use less expensive outworkers without creating tolerance problems when it came time to put the pieces together. The joke is that because they didn't change the rest of their cutting formula their jackets now button half an inch below the natural waist, and that's considered a feature instead of a bug. But I digress.
A high armhole helps keep the jacket collar firmly affixed to the back of a man's neck throughout a range of movement. A big sloppy one let's the coat move around, which is less desireable, but it's less expensive to make a bigger one and that's how ready to wear and made to measure makers have been doing it for decades.
Is this a ringing indictment of made to measure? Certainly not. I've seen too many bespoke Hong Kong jackets with high armholes that their wearers would have cheerfully have traded for a fix on the other fit problems. The only way to approach perfection is to pay for it and when that's not an option compromises must be made. And for made to measure, the scye's the limit.