I don't know how else to explain it, then, other than saying that the holes follow the grain. Say you have a plum sapling, 4" in diameter. If I split that small log end to end, because it is plum, it will probably spiral at least 90 deg. The belly side of that split will be mostly flat side to side, but twist longwise, and I'll have a half round stave 2" thick, that twists. So, this is an extreme example, but if I use my method, the holes drilled will spiral as the stave spirals. The drilled holes follow the grain. Then I come along with a hatchet and split again down along the holes. The holes guide the split. The wood splits from hole to hole following the grain almost perfectly.
So, now the limbs are @1" thick, follow the twist of the stave. Exactly up the middle of the back of this stave, at any point, regardless of twist, is a centerline that will be both the highest point on the crown AND one long line of uninterrupted grain fibers. Grain won't wander side to side or run off. Now, I come back with a rasp or whatever and remove any remaining wood between the little furrows, until those furrows disappear. Viola', even this crazy spiral limb is now a consistent thickness AND a consistent cross section. Strap it down with clamps that remove most of the twist to dry, cook the rest out during belly toasting, and make your bow.
Now, of course a spiral stave has it's own problems. But many staves twist just a bit one way, and then back the other, or have weird jogs in the grain before a knot or whatever.
