There are several ways you can use gadgets and one of those is to create one that can be distributed to other webmasters. The benefits are multiple. First, if you brand your website with a back link then every time your gadget is used it will create a back link to your website. Those are great for SEO purposes. Secondly, since the initial information within the iframe exists on your website, you actually help the search engines find you better and crawl your website more.
An iframe is created from existing information. The information is your site. Even after the iframe is placed on another website that information still exists on your site. And the back links from the other sites to yours will get the search engines to your site to crawl that information more often. The combination of the often-crawled content and the back links to that content (with highly valuable anchor text) can help your search engine optimization efforts tremendously.
Another way iframes help you is through marketing. It gets your content in front of more eyeballs. Every time a website uses your gadget you are getting your content and website in front of more human eyes. And that’s good marketing!