I've only seen a use for this in combination with the Trim Paths shape effect.
Say you have a shape that is stroked, but not filled, and you want to animate the stroke being drawn on. You can do this with Trim Paths.
When you turn on Reverse Path Direction, the stroke is drawn on in the opposite direction, from the 1st vertex.
Trim Paths does work with fill, but it's pretty strange looking on a complex shape. It would look pretty nice on, say, an animated pie chart, or a radar screen type thingy.