I have an app that displays a MapKit map with a Text as an a MapAnnotation. When the map is first displayed, the map is centered on the coordinates of the MapAnnotation and once things settle down, the CPU usage reported by Xcode's Debug Navigator goes to 0%.
If the map is dragged or zoomed so that the MapAnnotation is not at the center, the CPU usage goes up during the motion, but does not go back to 0%, but settles down to a few per cent. If you look closely at the map, you can sometimes see that the MapAnnotation is vibrating. Other map features do not appear to move.
I assume that the MapAnnotation is not tied to a fixed map location as are the map features and if the MapAnnotation is not at the center, its display position needs to be constantly recalculated.