I've never been one to plot out exact turn-by-turn routes and follow them on my GPS, but Strava Heatmaps was a great tool for scouting out routes for a vacation I took over the summer to an area where I wasn't familiar with the roads. There were a lot of 55mph roads with no shoulders in the area that would've really sucked to ride on and scouting out the heatmap ahead of time helped me familiarize myself with the area, avoid those types of roads and gave me enough info to feel confident just heading out and "winging it" on a few point A-B rides.
Strava heat maps also helped me find an awesome singletrack and gravel loop that I would've never found on my own just riding around.