SEO Advice: When To Use Subdomains

As a professional Search Engine Optimizer, I am frequently fielding questions asked by those lucky few who are new to the SEO field, and among these so-called "newbies" a recurring question often pops up - "Which of the following ways is best to structure site URLs?"

• www.site.com/subfolder OR
  
• subdomain.site.com

And so, it is with this recurring quandary in mind that I will attempt to answer the question, "which URL structure is best in terms of SEO, subfolders or subdomains?"
Short Answer: If the breadth of an issue or keyphrase will be covered in such detail that a new website should be constructed to best accommodate the content, or more simply, if the site’s graphical navigation will need to be altered, View the rest of this article