Like others have mentioned, most of the time you sew and subcut is because you'd be dealing with small pieces to start with and that is difficult doing on a machine, but it's not difficult doing by hand. I'd be another that would consider reverse engineering and sub cutting before sewing.
When I'm machine sewing blocks with small pieces, I usually cut them larger and sew, and then trim down. There is no way I'd try to sew a 1/2" finished HST on machine if I cut them at the correct measure to start with. But if I was hand sewing, I most certainly would cut them the correct size to begin with and not plan on trimming down after sewing.