What's the Difference Between Course and Compass Mode for the Map Arrow?

In the iOS version of the app, you can switch the map arrow between course and compass mode (Menu > Settings > Compass).

If you use “Compass” mode, then the arrow will rotate if you rotate the device.

If you use “Course” mode, the arrow will use compass mode (at low speeds), and if you go about 5mph, it will use the direction of travel to point the arrow instead, and the arrow won't rotate based on rotating the device.