They're only useful if they're real-time, they show you visually where the action is at and not at although they are not trade signals. Some heatmaps show the size and liquidity too while others are standard (everything is equal size, equal liquidity). A good heatmap would allow you to change the criteria. For example, you can see a heatmap based upon percentage change, points change in the past hour / day / week / month. Also, I've seen heatmaps on news/social trending, strenghth of trends and such. In addition, I've seen medical uses of heatmaps/treemaps of patients in a hospital by nurses/doctors caring for a lot of patients at the same time. Space Filling Visualization of representing large hierarchical collections of quantitative data. wrbtrader