In my opinion, animations should be like reverb in music. If it's noticeable, you're probably using too much (surf music excepted). A little bit of animation can smooth things out and enhance the experience with helpful cues. Too much makes the application a pain to use.
> he/she is already expecting something to happen
Just as an example, if I were to trigger Mission Control [1] in macOS without animations, it would be pretty jarring. In this case, I control the speed of animation with the speed of my mouse gesture, and it's quick enough not to get in my way, but animated enough so that I have a sense of continuity between my full screen web browser and the view of all windows on that desktop.
In contrast, the default minimize/restore animations in macOS are too long and cutesy for me.
> he/she is already expecting something to happen
Just as an example, if I were to trigger Mission Control [1] in macOS without animations, it would be pretty jarring. In this case, I control the speed of animation with the speed of my mouse gesture, and it's quick enough not to get in my way, but animated enough so that I have a sense of continuity between my full screen web browser and the view of all windows on that desktop.
In contrast, the default minimize/restore animations in macOS are too long and cutesy for me.
[1] https://en.wikipedia.org/wiki/Mission_Control_(macOS)