On several occasions I've researched twitter handles (user names) before selecting a name of a blog or website. I did not want to use a name that is also being used by someone else.
Exclusitivity of name can prevent confusion.
On Facebook there are several people using the name Christian Post that are unrelated to this website. A couple of years ago this created some confusion. However, now Facebook shows The Christian Post as its top result and I only see multiple Christian Post users if I click the link that say, "See more results for Christian Post."
When starting a website, for branding purposes it is best to claim the same name on Facebook, Twitter and other social media websites. That way a critic, opponent or troll can't claim your name and spread misinformation in your name.
Recently Search Engine Land featured an article on reputation management and recommended the use of KnowEm.com to search through many social networking websites at the same time see if a username is available.