Yes you are missing something. The purpose of this library is to decouple the "description" from the "computation" itself. I usually call "separating the _what_ from the _how_".

Essentially they construct an AST for whatever services that need to be called. Most of the time they then simply "interpret" the AST with the lower-level Finagle constructs. But, and that's actually the big point, they can use _the same code_ with a different interpreter to generate a GraphViz representation for visual inspection. This super helpful once your call graph becomes more complex .. Another possibility is to write an optimizing interpreter etc.

Anyhow, what I find a bit sad is that they didn't leverage the Scala part if Finagle more .. this would be a prime example for a Free Monad () based DSL. That way they could have avoided writing 10s of classes with less than fortunate names.

() might need a Free Applicative part as well since they inherently want to have parallelism expressed in the language