SkyLight should be Stationary or Movable

Following this UE4 Neutral Lighting Scene Setup and confused when the author says your SkyLight should be set to Movable.
Shouldn’t it always be Stationary? I’m confused.

The HDRI has a movable skylight with it by default, and the HDRI in the video is mostly neutral colors in the backdrop and on the ground image, so it’s remaining neutral coloring from the skylight capture. If it was stationary, I think it would be the same, so I don’t understand why it’s required to be movable either. Is there a color or contrast difference based on the cubemap for stationary versus movable? It could be easier to modify the coloration from the skylight cubemap’s capture when it’s movable than if it’s stationary.