Some tiny amount of animation is needed to show that the system has responded.

I regularly use a website in which a submit button does not change state in any way. It is indistinguishable from the click having gone to /dev/null. And the completion of the action takes a copule of seconds.

It's literally, "no response ... few seconds ... oh, done!"

If the button simply responded in the usual way, like 3d poppin in and out effect, it would be better. The UI can change state also to show some "wait ..." text.

These are examples of animations, just not progressive/persistent.

As a kid I liked the interfaces that lagged badly, but still accepted input perfectly.

It felt like I was racing. Type the whole message before the screen updates? Check.

I miss AOL sometimes.