My point originally was about this statement of yours, that is purely conceptual and you skew the discussion to address the other part of your comment (or you through that was the point but didn't explain so in your answers)
But anyway, one assumption is that every game should have a fixed gamestep, in many single player games (real single player games) you don't want to do that, because is preferable that the user can see the ball coming to the player than to magically appear behind the player even if that is "timely correct"; the ball/interface going slow is a lot less frustrating that losing without realizing why. Platformers for PC with (virtual) high speed movements come to mind as a common example of this.
Even multiplayer games suffer of this; in most online FPS if the server suddenly slows down all the players start experiencing lag and everyone looks like they are "teleporting"; with a not-fixed-timestep you could slow everyone down so the problem becomes a lot less frustrating because the player still have complete control and understanding of their in-game character; just a bit slow-mo until the server speeds up to normal. The teleporting should be used only to sync with the server when the client connection is the one with problems updating.