It depends on your definition of "useful." If you look at a single GAN-generated image in isolation it's almost certainly "useless" for most definitions. But if you need a bunch of faces, sneakers, buildings, whatever, and you want to be cognizant of people's privacy, and you don't mind the occasional weird image artifact or completely fake-looking image, these can be good alternatives to sourcing a large number of real images.
So, for example if i was creating art or designing something, say i could use one of these generated sneaker images instead of a stock photo (could be useful, right).
Now the question is, since the training material were images of copyrighted designs/shoes could this get me in trouble?
I feel like there are many cool uses for generated stuff such as generated music or generated code also, but ultimately the uses are held back by existing laws and regulations around copyright and so on. So it really doesn't solve anything that also wouldn't be solved by just getting rid of copyrights entirely.. (sorry, just thinking "out loud")
"Just" getting rid of copyrights entirely isn't going to happen so it's kind of pointless to speculate on that front...
I don't think it's a foregone conclusion that generated images are subject to copyright even if the model's source images are copyrighted. You can make an argument that if all the source materials are subject to the same copyright, the generated images could be. But even in that case the copyright applies to the source. It doesn't apply to the next step (at least not explicitly). It depends on the legal definition of derivative work, if these images even qualify as a derivative work, etc.