-all layers with normal speeds set 1 and auto speeds set 0 will be moved the same amount of tiles to the top and left, until on one of these layers a tile hits the layer border (the layers with normal speeds 1 and auto speeds 0 depend on each other)
-all layer dimensions (so how big each layer is) will be lowered to the lowest amount of tiles possible without removing tiles (the layers are independent here)

this way the level is moved to the top left corner and the layers are changed to the minimal size, so that if you walk at the edge of a level the screen doesn't scroll anymore, and you'll have a better view of the level.