> Obviously not used in competitive racing, but very useful recreational for track driving.

While actual race cars don't have turn indicators, actual headlights are common in some racing classes (especially for endurance racing), and multi-class races are common (where multiple different categories of cars are racing on the same track, often with _very_ different top speeds). Flashing headlights is a common way for a faster car behind to indicate to the slower class of car ahead that they're coming.