Faceted nav also has SEO benefits, in that these facets serve as keyword-rich links and 'tags' of sort that add semantic relevance to the products contained within each facet.

But it's not all good news: faceted nav can also result in problems with indexation, specifically duplicate content issues. As sometimes many different facets will contain nearly identical sets of products with little variation, search engine spiders could end up in crawling loops where they crawl slightly different product lists over and over again.