This feature will resolve most double indexing problems by forcing all links to your http://www.domain.com version. With a Yahoo! store other variations of your domain can be indexed including - http://store.domain.com and http://domain.com, which can really hurt your SEO efforts. This feature will make sure that once you publish your store that all links in your left side navigation, top navigation, footer, items, and sections are forced to your http://www.domain.com version. Save yourself from double indexing penalties by investing in this feature.