Question: What's the difference between hand-sewn and machine-sewn seams?
Answer: Hand-sewn seams are created by a single thread running through fabric like a wave. Done right, they lay smooth and do not pucker. Hand-sewn seams handle stretching well, and spring back into place after movement. Hand stitching is advantageous in curved areas like armholes, collars, and waistbands.
Machine-sewn seams use two threads crossing over each other through the fabric. They are sturdy and more precise than hand-sewn seams, but the extra tension created by having two threads pulling in opposition can lead to puckers in the fabric on curves. Machine stitching is advantageous in straight-seam areas like trouser legs, where it can be more durable and cleaner than hand stitching.