Reasons to alter from Shoulder. Maintains the original proportions of the jacket, including sleeve pitch, shape, and buttonhole placement and functionality. The sleeve seams remain aligned with the original jacket design.
But it’s more complicated to achieve a seamless result and much more costly and labor intensive.
Alteration from the sleeve is faster; less costly. Although button functionality may be lost, this type of alteration may be necessary for two reasons :
1) if you wish to alter more than a couple of inches. Altering more than that from the shoulder isn’t recommended.
2) sometimes one needs extra circumference in the upper arm. (alteration from the shoulder may tighten the upper arm area).
Chanel tailors (and experienced third party) mainly alter from the shoulder. If a garment needs to be taken in, it’s my understanding that the tailor will open up all the seams and take a bit from each rather than simply the sides. There can be up to eight seams with ample seam allowance in a Chanel jacket which is why some garments can be adjusted up or down.
The chain weights are a PITA. Once functional, now decorative, they have to be cut or partially snuggled into the lining, and they are sewn back in by hand
ETA: in some garments (like some Hermes jackets) the sleeeves cannot be altered via the shoulder (no seam, like a dolman sleeve) or the sleeve has details like a zip run up most of the arm. Or, both. One of my dream pieces, a runway piece was like that. Also, as in another piece, if a printed silk pattern has a border, this can also be very difficult to shorten bc too much is lost and cannot be pieced together.
In men’s tailoring, some of the most beautiful jackets are without lining or have a half lining to preserve the shape. This is bc full lining can hide a messy interior. A jacket with entirely visible seams has to be finished perfectly.
