It will be very useful to have x and y scale factors for images in atlas setting. If you have, for example image like 2000x2500 pixels it will be using 2048x4096 atlas, but if i scale it a little in y size - it can fit to 2048x2048 atlas. The proplem is that if i scale original image - i lose original image size and have to backscale game object to set original size. Another way will be to scale images in atlas and it does not affect to logical image size, but only quality.
Here are examples:
It very useful in any spine models and any backgrounds (huge backs for modern phones)