Here is how I use the Strava heat map data when I am touring...

- The primary case for me is entering/exiting a larger and unfamiliar urban area. I've found that often there is a "doughnut" around an urban core where I need extra caution. In the city center, often the speeds are low (or they are clear expressways) and while traffic is dense there are often multiple roads to adjust. Far enough from the urban core, densities and traffic volumes can be less.

- In rural areas, I am more likely to consult a state bicycle map that shows me traffic counts and rough shoulders. I also am more likely to consult with state DOT to look for construction projects because that can really reconfigure some of these routes. Rural areas can also be a bit different in different parts of the country. In western or less populated states, there may be fewer road choices and often for a extended trip I'll look for a major US highway. In more populated areas, there can be more roads even in rural areas.

I think it is a useful tool in the tool box though like anything it can be overdone if that is only thing you use.