If you've got a retail site with a large product catalogue, you already know you need to make sure your customers can find what they need without too much guesswork. Your most motivated customers are the ones who use the search function on your site. In fact, they're twice as likely to convert because they know what they're looking for.
Offering faceted navigation helps all of your customers, but it especially helps your searchers. Facets help them narrow their options and find what they came for without having to guess at your catalogue descriptions and structure, or do too much filtering and browsing.