A machine lockstitch uses two threads that loop around each other. If one breaks, the seam can run like a ladder in a stocking. A saddle stitch uses a single thread with a needle at each end, and every hole is passed through twice.
The pricking iron
Before a needle touches the leather, the maker marks the stitch line with dividers and taps a pricking iron along it. The iron sets the spacing and the slant of every stitch. Ours are set at 3 mm.
If a saddle stitch is cut, the stitches either side hold. That is the whole reason to do it.
What it costs
Time. A wallet takes an afternoon; the handles of a tote take about two hours. We stitch by hand where a seam carries weight: handles, straps and tabs. Long body seams are sewn on a machine, and we say so on each product page.