The primary advantage of hand sewing over machine sewing is you can completely hide the stitching when hand sewing. If you ever get a chance to see a Tewksbury or Lare kilt up close you cannot see a single stitch.

If a line of stitches will never be seen because they are covered like the first row sewing a waistband on, where you will then fold the fabric over and cover the stitch line, can be done with a machine and I know quite a few kilt makers do so.

The other reason to hand stitch is the life of hand stitches is very long compared to machine stitches. In machine stitches you use two pieces of thread, one from the top and one from the bottom. If one of those lines of stitches breaks or wears out there is nothing to hold the other thread in place and it unravels. When the unraveling starts it happens very quickly. I have seen an entire pleat come unstitched in just a few moments causing a rather embarrassing moment.
In hand stitching it is one piece of thread worked over and under then over again. Even if the thread breaks it tends to stay in place. Or if it starts to unravel it is usually caught before going too far and can be fixed easily.

The thing that amazed me was how fast a good seamstress can do hand stitching. When Barb T. was here at Kilt Kamp I watched her sew a pleat almost as fast as I can do it with a machine. And every stitch was perfect. Completely invisible and exactly evenly spaced. I just sat there with my mouth open and eyes bugging out. And she was holding two pieces of fabric, folding them with a perfect taper and her alignment of the Tartan pattern was never even one yarn offset.