Volume Flow seems to diverge from price when the market is oversold. In other words, the yellow lines dictate when the hype cycle fueled by harmful investors emerges (a secondary, greed-fueled cycle, as opposed to a momentum-fueled run), and the selloffs from disciplined market makers begins. Don't be like the traders in the chart that kept buying for a year after the divergence, unless you plan to hold long-term (5-10 years).
When the signal trend drops below ~-2.5, the price only recovers when the signal confirms to 0 as the price increases. (ie, no more divergence, we get a new cycle)