The two-piece sleeve has seams which appear at both the front and the back of the arm. The under section of the sleeve will actually be a tad bit smaller than the upper part of the sleeve. This will make the seam appear less noticeable on the finished garment. The seams of the two-piece sleeve also fall slightly off center from the front and back of the arm. With the seams falling in the offset places, they are then less apparent when the apparel is worn. This strategic placement of the seams allows for greater range of motion.In my opinion, the two-piece sleeve is the BEST option (for ME) for jackets and coats because it gives a more tailored appearance.
I'm currently working on a jacket now. The pattern only offered a one-piece. And the look that I am going for is nice tailored sleeves with a vent. I thought for a split second to try and convert the one-piece. That seemed really, really daunting to me. So I ended up jacking a sleeve from another pattern that I liked.
Do YOU have a preference on jacket and coat sleeves?