Another thing I like about alt-text on pictures, even if nobody sees it:
It forces me to think about why I am sharing an image.
What do I want the audience to get from this picture: what details will I focus on and what is irrelevant; what mood am I aiming for; is it factual or shitposting or an anecdote or a cat? (It’s probably a cat)
If I don’t know these things… then I don’t post the picture.
And it is for these reasons that I usually check the alt text on other people’s pictures - what was it about their image they wanted us to know?