Done as part of an Expert Review but can also be done in more detail as a separate piece of work, these are ideal for feature-rich sites with a wide range of established competitors (e.g. : retail/ecommerce/service-based) to produce a bench-mark for ongoing enhancements.
By comparing your site against other best-of-breed sites (from your industry and from other fields) we gain an understanding of the current condition of your site and of its standing amongst its peers.