Pros, more fps on low end hardware.
Cons, worse image, ghosting, blur, artifacting, lower overall performance because devs rely on upscaling.
It's existence is a crutch. Games should be made properly and not rely on ML upscaling for meaningful performance.
Hardware is insanely powerful at the moment, the problem is time isnt spent making the most out of it anymore, which then increases demand for more powerful hardware (that we dont need). The sales loop for Nvidia, except now they want to sell you ML optimised cards, which cost more.