You can also do curves with the pen tool, not just straight lines as that tutorial shows. It's a tool probably taken from adobe illustrator, since it's a vector tool. Good job its in PS too, because I've got no clue how to use illustrator. Really handy for anime hair, which is usually flowing in gentle and consistent curves. You can cover a lot of ground quickly outlining curves with the pen tool as opposed to lots of jagged straight lines.
But thanks for that tutorial "The easy way to get rid of annoying darkght edges". Usually I just ignore those lines, since imo they don't look that bad, but its still handy.