Self Type in Scala

Self Type as Dependency

Have you used this in the wild? It seems interesting, but not sure when I would use it. Perhaps if I don't control the Vehicle trait, but I want to extend it? But Scala has Extension Methods to do this as well. When should I use one or the other? I haven't had to use Extension Methods either. Perhaps this is more for building Libraries and not Applications?

Self Type as Tagging

This remind me a lot of var that = this; in JavaScript haha, brings me back. :-)