This is useful in a pinch, but transitioning a 100px high element from max-height 9999px to 0 means there's going to be a huge delay while it's transitioning be

This is useful in a pinch, but transitioning a 100px high element from max-height 9999px to 0 means there's going to be a huge delay while it's transitioning between 9999px and 100px followed by a very fast transition between 100px and 0, which is usually worse than having no transition at all.