re: Why Scribe Marks for Dove Tails?

Scribe lines (knife cut or marking gauge disc/point) are for marking but also used to precisely let the chisel edge in.  I also use scribe marks for this reason to precisely delineate the edges of a hand chopped mortise. In the case of dovetails, it would be the exact position the chisel needs to begin its cut and eliminates any issues with "what side of the pencil line to cut". A pencil line is much fatter than a scribed line.