[openfuture]

I think they come in handy when you've got some functionality that has to happen in a context that you can't easily move between function calls... Then you benefit from the ability to template into the description of that context some actions to perform _before_ you enter into the "black box".

That's pretty abstract but honestly its not really such an earthshattering feature. I'd argue it's pretty much necessary for any "final" programming language to be infinitely metaprogrammable (i.e. a lisp-3) but we don't have a mature language like that yet. Probably it will arrive from laskell/hisp kinda synthesis.