Outside of dedicated notification areas, a GUI should only change state in response to user action. Because the user requested the state change, they naturally know how it changed. This means any animation is a redundant waste of time.

The notification area doesn't need animations either, because a GUI is only appropriate for displaying non-urgent notifications. If something really needs urgent attention, you need alarms and flashing lights, not an animated "toast".

Do you have some concrete examples?

"Back-in-the-days" you'd click and stuff would instantly happen, and I don't remember anything being more difficult to visually interpret.

On my Kubuntu desktop if I disable all animations (the whole compositor) I don't feel there is an increased cognitive load of rescaning things - but maybe it's my preexisting memory of the UIs and certain baked in UI expectations. Maybe this animated stuff helps people that are computer illiterate? (software made for the lowest common denominator)

This isn't true generally. I am personally far more comfortable with disabling smooth scroll. It has more to do with your mind's expectations. Which can vary between people. Some people expect smooth and others don't. Motion itself isn't necessary.

The only time I have to "rescan" is if I input a scroll and anticipate a scroll and it doesn't scroll. It has nothing to do with motion. In fact, in that case, I "rescan" even though the page hasn't changed, but because it doesn't match my expectation that it would change.

The OS shouldn't be making many big changes that force me to reorient. When I'm moving between different UIs I often want to compare them; animations make it harder to compare state A to state B. I can detect very fine differences between two images by switching between them within a second, if there's a 1-second animation it not only means it's going to add a second, it adds a bunch of visual noise which might make it impossible to be able to distinguish what's an actual difference and what's just noise introduced by the animation.

Ah yeah, that makes sense, but I still feel like there's room for a little more discretion.

https://tonsky.me/blog/every-frame-perfect/toolbar@2x.mp4, for example

I don't think I would have to rescan the entire page to figure out where things were afterwards. Everything's shifted to the right, just like when I open my browser bookmarks.

True in 3d CAD when switching between work planes. I can't think of another application.

>Motion is critical for reorientation after transition.

The only case I can think of where this is true is on scroll, and that barely counts as animation. Anything else is an irritating waste of time.

The absolute worst offence is animating page content on scroll. Great job making me wait on pointless nonsense while scanning your website for the bit I'm looking for. People who do this should be sent to reeducation camps. Both for the animation, and for disregarding 'prefers-reduced-motion'.