[plt-scheme] What is the role of promise and force?

What is the role of promise and force?

This weekend I read the R5RS spec. Before then I hadn't heard anything
about promise and force, in other words, they don't get blogged about
or written up much. Why not? Are they important? For what kinds of
things are they used?

It is suggested that they allow for you to write programs in a true
functional style. Are they similar to the goal of Haskell monads in
that they let you "do it all functionally?"