[majewsky]

> Honest question, is there any evidence that shows the usability is _worse_?

It is obvious that usability will suffer when you cannot fit all the required functions into the screen real estate. Now, since we're talking about websites, which usually have a rather low function density, that's not necessarily a problem. But try to apply this design advice to more complex web applications, or to professional software like Photoshop or Blender.