The approach I've adopted is based around a simple single level control workflow. It takes an input and then based on that sequentially determines what should happen next. It triggers that by calling another workflow using an x-callback URL.
I can't find much practical use for it and it is quite complex to grasp what happens underneath, but interesting if you want a modular approach to your workflow. Here's a video so you can see his examples in action. Stephen has even more resources for Workflow, so be sure to check his blog.www.thoughtasylum.com