[willtim]

Yes it is a bit unnecessary in the simple list example above, but Endo becomes useful when using arbitrary nested Foldable structures and when composing monoids, e.g a pair of monoids is also a monoid. In other words, it becomes useful at scale.

To quote from Paul's post: "The trouble is that very often, the sorts of examples that are easy to discuss aren’t of sufficient scale to reveal any major differences between A and B."