Prioritizing clicks refers to display click ads, although advantageous by being ‘simple, fast and inexpensive’ rates for display ads in 2016 is only 0.10 percent in the United States. This means one in a thousand click ads are relevant therefore having little effect. This displays that marketing companies should not just use click ads to evaluate the effectiveness of display advertisements (Whiteside, 2016).
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.