You're going to get shading errors and all kinds of problems with the 3rd example. Try to unwrap it, normal map it and put it in your engine of choice and you'll see.
In the context of long thin triangles, it refers to the waste of shading processing when you have a surface that's not triangulated with care. As a necessary step, a GPU will process triangles in a way that is efficient when rendering the interior of triangles, but not so efficient when rendering the edges of triangles.…