There are advantages to reprogramming the screen dimension to match the Spectrum's.
* The gameplay is similar because the player sees the same amount of map and there are the same number of enemies and they move in the same way.
* Graphics/levels would not need to be designed for a wider screen (320 compared to 256)
* For the Amstrad, a 320x200 screen normally takes 16K, but when reduced in size it takes 12K.