Multiple layer merging
Multi layer merge
The graphic card don't known what is the changing layer, what is pure static layer. Then It redraw each layer above the other.
It's you in programing to group the static layer, merge it to prevent the GPU do the multiple same draw (You don't use the CPU/GPU to merge always the static/same image to do the same result).
For CatchChallenger and official datapack, this improve the framerate by 3-6x depending of the map. On Optimised map, this improve the framerate by 2-3x.