my two cents, that's a terrible article. Showing a long line on the surface of a sphere, spiraling toward a pole, says visually "this is clearly a pretty dumb direction to point your boat". There must be some benefit to navigate this way but the article buries that (if it gets to it) in some pretty advanced math, partial derivatives of trig equations. I doubt anybody will come away with an understanding of why rhumb lines are useful.
> There must be some benefit to navigate this way
This is what happens when you keep your boat pointed at a fixed compass heading. I don't think anyone is intentionally sailing in spirals.
your comment, like the article, has shed no light
Well then I'm afraid I'm not entirely sure where the confusion lies. Perhaps you could clarify?