> What is the actual use of this?

From the article:

"Our analysis of road segments in California and Virginia revealed that the number of segments with observed HBEs was 18 times greater than those with reported crashes. While crash data is notoriously sparse — requiring years to observe a single event on some local roads — HBEs provide a continuous stream of data, effectively filling the gaps in the safety map."

So we don't have to wait until an accident actually occurs before we can identify unsafe roads and improve them.