Do I need RDF enabled on a normal site?
As far as Google is concerned if your website is well structured it will be easy for crawlers to crawl your website.Morever Google Rich snippets uses RDF and it needs every site to be RDF structured if you want to enable rich snippets for your website.

Drupal 7 rich snippets and RDF


  So Unless you have any problem with RDF module enabled why you need to
  disable it?