Not so much a mechanical preference, it is a natural outgrowth of making the blade from a layered piece of metal. Forging induces waves of various sorts in the layers, which makes the sides of the blade look wave-y. It is usual to leave the edge fairly thick so it will withstand quench-induced stresses better. Once the blade is heat-treated, the edge is thinned down to where it will cut and this abrasion cuts across the layers, revealing the lines along the edge. You can tell how close to shape a blade was forged by how wide the zone of lines is. The effect is visible on wootz blades as well. There are ways of getting around the effect, but for most ethnographic blades the maker was not worried about it.
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