Completion rate: Completion rate is the number of people who completed your video divided by the number of people who played it. Completion rate, and other engagement metrics, are a great way to gauge a viewer’s reaction to your video. Do you have a low completion rate? Are people all dropping off at a certain point? This might be a sign that your video content is not resonating with your target audience.
Another reason is that if you're using an image as a link, the alt text for that image will be treated similarly to the anchor text of a text link. However, we don't recommend using too many images for links in your site's navigation when text links could serve the same purpose. Lastly, optimizing your image filenames and alt text makes it easier for image search projects like Google Image Search to better understand your images.