High cut armholes fundamentally make the fit, comfort and wear of a tailored jacket far superior than that found in a lower cut armhole. Not only does it counter the messy silhouette associated with the big baggy sleeves and ill fitting shoulders of a lower cut armhole, high cut armholes allow freer movement of the arms, independent of the body of the jacket.
So, doing practical things like reaching for things above your head, tying your shoes, driving or even just sitting at your desk, high cut armholes offer a great deal more fluidity and flexibility of movement. This becomes a particularly important consideration when buying custom suits and tailored jackets that you plan to wear to work every day.
An added benefit for men with a slim build is that high cut armholes allow the jacket to fit more closely to the chest without bunching. Also allowing for a narrower fitting sleeve, the high cut armhole avoids excess fabric appearing like wings under the arm. This also avoids the creation of a pulling distortion of the cloth at the shoulder.
Low cut armholes are the norm in ready to wear suits, with the wider sleeves and lower cut affording the ability to accommodate men of a variety of shapes and sizes. This approach obviously makes sense for the mass market. However, having a low armhole also means that when you raise or move your arms, your jacket lifts and moves around with them. Not the best look.
High cut armholes are just as important in shirts for the same reasons. Wearing your bespoke suit jacket with a ready-to-wear shirt will lead to a bunching of the shirt cloth at the top of the arm. This is because the shirt will be cut to a more general, mass market accommodating fit.
So, the message is clear. If you want the ultimate in comfort and a stylish silhouette then the combination of a bespoke shirt and suit jacket, both cut with the traditional high armhole, will always be your best bet.