>Personally I am not sure why anyone made a flat sole spokeshave at all?
>Anyone know?
>Anyone find times when the flat sole really shines above a round sole?
I'd say they make flat soles -- the most common sort -- because of the primary work they were supposed to do, which is shaping wooden spokes. The flat sole makes it generally easier to shave a straight line when rounding things longitudinally. The spoke shave, as the name shows, started out as a wheelwright's tool, and got hijacked by more general carpenters, coach makers, and the like.
If I'm doing a chamfer or shaving a round, I most likely will reach for my Stanley 54 or 53. Use them more often than any other shave I have. But I have other flat sole shaves that I can also use for these tasks. The first time I ever used a spoke shave was to radius the corners of a cutting board, and a flat sole was the tool I was given to do this. For me, the flat sole gives me a little more control of the cut.
For concave surfaces, nothing works like a rounded sole. Nothing else actually works at all, and I have several round soled shaves for this kind of work.