[tel]

It's useful for more general folds over more general types. If you have a tree structure then you might not want to fold from the left or the right but instead in multiple places in parallel and then combine them at the end

    * + (* + (* + (* + (* + (* + *)))))   versus
    (((((* + *) + *) + *) + *) + *) + *   versus
    ((* + *) + *) + (* + (* + *))

[SamReidHughes]

Oh God, right. The changes over the years have left me bamboozled. Is (.) fmap yet?