Oh, I don't doubt the significance of channelling. I just wanted to make sure it did not relate to the stitching I often see around the outside of the sole visible from above the shoe. What purpose does this serve?
Well, that depends on the method used to construct the shoe. If it's a Goodyear-welted shoe, then the stitching attaches the welt strip to the outsole:
If it's a Rapid-constructed (or rather, a Blake/Rapid-constructed) shoe, it will lockstitch the topsole to the outsole:
Oh, and it's also done for looks.