Oh yeah, definitely. For me the usecase is infinite scrolling, where you buffering offscreen images to allow you to continually flick through an image feed without having to "wait" for a preview to appear. Although you can do this without JXL, its a much more fluid experience with the progressive download - especially if you micromanage the behaviour of the network requests (i.e. progressive throttling of offscreen images past first frame). Lower filesize over JPEG is also a benefit there as you can more quickly resume the load of the higher fidelity frames when in view.

Current browser support where available is a lot more restrictive TBH, as you dont have any control over that behaviour. But outside the browser its solid gold.