One advantage that gives you, is that you can easily define a monad on top of that and not worry about monad transformers. Jane Streets async library does that

One advantage that gives you, is that you can easily define a monad on top of that and not worry about monad transformers. Jane Streets async library does that in its Deferred module https://ocaml.janestreet.com/ocaml-core/111.17.00/doc/async/#Std.Deferred https://ocaml.janestreet.com/ocaml-core/111.17.00/doc/async/...