Content gating is required if you are going to sell content on the site or require a registration to access content.  A key feature of the Content Gating module is its ability to block content to non-paid readers but make it available for SEO.  This solves a common problem of paid sites where none of the content can be found by Google searches.  The Content Gating module is integrated with the Ecommerce module so that you can define pay per view products, memberships, and subscriptions.  Included is a My Purchases page where readers can easily return to content that they have purchased.