Buying a domain name for a blog

Usually when your blog starts to become famous or you get some high traffic, the idea of buying a domain name for your blog must have passed through your head ...

You have to know the advantages and disadvantages of this idea before you decide any thing

A Advantages :
1-Buying a Domain name for a blog is the best SEO you can do , yes ... all search engines usually prefer a website on an independent domain .com, .net .org .... rather than any free hosted site
as, ....
2-Surely more respected from visitors
3-Higher traffic rank. the reason of this is not so obvious to me but it is so difficult for a blog on free hosting to get among the top 100,000 websites

B Disadvantages :
1-You lose All Back links You Made Before , yes this is the major disadv., you may not lose links as blogger or the host will redirect the old URL to your new domain , BUT Your Page Rank and Search results will retreat and may be unpleasant at first
2-Visitors who bookmarked you at first may not be more able to reach you (Redirection is not always guaranteed )

So the overall Advice is to buy a domain name at first , when you start building your blog
the most favorite domain seller if GoDaddy