What is the difference between really starting a composition and firing manually with the start fire node?
I’m driving slightly mad!
When you start a composition, the Fire on Start node fires an event. When the composition is running, you can right click over the Started output port. You will see a popup window that includes the option Fire Event. This option will allow you to manually fire another event from this node. I find manually firing events from the Fire on Start node a good way to see how some changes I’ve made to the composition will affect the result. Hope that’s helpful.
You can also Cmd+click the “fire arrow” of any node, saving you precious right-clicks.