I will try in my words to describe how I use it and why I think it such a great tool.
I am trading a lot and always have this problem to start or end the trade at the right moment, of course, I use technical analysis, supports, resistances, fibo and all these stuff, but heatmap is just the right tool to see were the biggest buy and sell pressure is because it displays all buy and sell limit orders in real-time.
Now, I will show some screens of the BTC/USD chart on a different time frame with an aggregated heatmap.
Here we can see how price accepts and bounces beautifully back from the high supply pressure, as a trader looking at the volumes and price action, you can really perfectly time your trades.
Another great example of a different situation on a smaller timeframe, the price goes all the way down, to finally bounce back up from the buying pressure.
If you were shorting you can stop your trade perfectly and maybe even go long just after if day trading or scalping, because such patterns that the price bounces hard from big buying and selling pressure are common.