OP here. My original submitted title was: It never makes sense to use foldl on lists (in Haskell); first line of the linked content. But someone dropped the bracketed content.
But foldl vs. foldl' is more about a badly-optimized implementation detail than anything else. It's very fair to qualify it as "in Haskell".
> foldl/3 is tail recursive and is usually preferred to foldr/3.