re: Why Scribe Marks for Dove Tails?

Late to the party... It is easy enough to mark out everything with pencil first and then mark just the waste area with the marking knife.  The reason to mark with a knife is so you can use a chisel to first cut back to create a knife line which creates a knife wall that helps  prevent the chisel bevel from causing the cut to move back and creating a gap.   I learned this from Paul Sellers' technique.