Why do you use helper edges, instead of just extruding and scaling?

I’m not exactly sure what you mean…helper edges maintain a sharp edge for use with subdivision surface smoothing (subsurf). Extruding and scaling doesn’t serve the same purpose. Though I may be misunderstanding the question.

Oh oh, my bad. I did use the term “helper edge” in the video but incorrectly translated that to “holding edge” – 2 very different things. I’m the causer of confusion here!

So in that specific case, the oblong nature of the shape means scaling would not produce an even bevel; the top/bottom edges of the bevel would be a shorter distance than the side edges. Using ALT + S to push the helper edge according to the normal is what gave me an even bevel.

Though in hindsight, the technique in the video is not the optimal option. I could have filed the face, extruded slightly and then used the bevel operator to get an even bevel. That would have likely been optimal.