Right now there is a bit left to be desired when it comes to lemmys accessibility features, but it’s a good idea to be mindful of the fact the fediverse and its platforms tends to have pretty universal accessibility features that will likely come to lemmy sooner rather than later
I can’t really think of a case where a post’s image isn’t relevant to the associated discussion. Even if it’s just a nonsense post with an unrelated image, knowing what the irrelevant image is about would help make sense of the discussion.
Not enough info is better than nothing. Because if it’s nothing, you can’t tell if the person who shared the image is lazy or decided the alt text wasn’t necessary for this particular picture