[bgirard]

I proposed will-change a decade ago when I used to work on the rendering stack at Mozilla and also tuned frontends.

In some circumstances the heads up is totally required. For example if you're on a low spec mobile device with a relatively high resolution display, you're in a situation where you can't build a layer for an animation you didn't expect. And your memory footprint is so low so you don't want to be building layers unless you need them. If you don't have the heads up then you're going to drop the first few frames of the animation and the experience is going to be janky every time.

If you're in a situation where it's not required, then I would advice against using it FWIW. I still work on optimizing web frontends and I almost never use this property because I rarely need it.