Hi,

Example: 

If you upload an image with size: 3000 x 3000 px

We can't use the original image to display it in all places because it's too heavy to load.

That's why we need to crop it to different image sizes, smaller to display it on places on the website to make it load faster.

If you disable an image size - if a place uses this image size, it can't find the image size to show and will be showing the full image.

Best Regards,

PenciDesign