The ability to disable unused image size.
When you upload an image using Media Uploader, WordPress generates multiple copies/thumbnails of that image.
Unnecessary additional images are eating up your server space and slowing down your site.
"The ability to disable unused image size."
A theme does not know which styles and options you will use, and it generates all sizes so that all functionalities will work properly.
Currently, there is no setting to disable them, but I will pass it to the dev team, and we will look at how it could be handled.