Images are optimized for different screen resolutions, but not compressed in size from what I have been able to figure out in trying to synthesize many threads and replies in the community. See here from yesterday:
I have to say, I agree about the storage concern, but if Glide solves that, they have to do so without compromising resolution for desktop users. I’m not a developer so I don’t know if you can compress size to store, then decompress when image needs to be optimized for larger display - I hope so as that would be the ideal flow. 
@david If Optimize and Size Compression are two different things in Glide context, it seems there is still confusion as to the storage issue and the sometimes synonymous use of these terms…And if it already works as I suggest is ideal, then the app makers are finding otherwise.