I have seen this a lot, but have never read anything on it. For SEO purposes. What does http://digitalpoint.com have over http://www.digitalpoint.com (example) ???
Nothing. Consistency matters - otherwise people will link to different URL versions and that way incoming link juice will be splitted. So, better to choose preferred URL version to promote, for internal linking etc. Second version could be 301 redirected to preferred URL via .htaccess.