[coolsunglasses]

Twitter's finagle is a good example.

Anytime you need to perform more than one interaction with external services in parallel, it's a lot easier to wrap the results as futures and interact with the promise objects than to cope with callback spaghetti.

This is particularly critical anytime you're working in an SOA environment.

I could see why it's easy to believe that you don't need promises if you're averaging 1-2 database queries and 0 API calls per web page/API call reply, but once your scenario gets even slightly more complex - you're fucked.

Promises are one of the big reasons I like Clojure's concurrency better than Go's.