I have fairly complex flows, sometimes involving dozens of frames. When I test the flow in prototype mode, I would like to know whether I have visited all the frames of the flow, or only part of them. In case I missed some frames during my test, I would like to understand which ones, so I can complete my exploration in a guided way.
An analogy that pops to my mind: Your keyboard shortcuts pane gives me a very clear idea of which shortcuts I have used before, versus the ones I never tried. This is highly useful!