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.
If you do great work with your search engine optimization (SEO), it could mean a significant amount of revenue for your business. At the same time, however, it is also an ongoing initiative. Once you generate a steady stream of traffic from SEO, you need to constantly be maintaining and improving your SEO in order to keep those rankings you worked so hard for.