If your workflow needs x number of Inputs, it will need those x inputs both from GUI and API for execution. The GUI has some background magic-logic that makes things easier for you by providing you ready-to-run default inputs. You change one input( Security Zone) and rest automatically gets filled.
But API is an advanced call, it will not have that magic logic for your rescue as you do in GUI. You will need to create the x-inputs in a formatted XML body for the worklfow to execute. This can be a difficult error prone task and it gets complicated if you have many and complex type of Inputs like Table or Query-Multi select.
So here is your resque ticket. For all the GUI lovers, use GUI to provide all your inputs. And get the equivalent XML formatted body with all inputs within seconds, Ready for execution using the API. Now just use it.