For users ssing a subdomain for a blog site is perfectly OK, however there’s a search engine benefit advising against it. Search engines see subdomains as separate from the main domain, and subdomains need to earn their own credentials. Whereas subfolders inherit a lot of benefits from their “parent” (and vice versa).

Sites like blogspot.com and wordpress.com are a perfect example for this behavior:

robin.wordpress.com is not affiliated with wordpress.com. Neither are 99%+ of the subdomains on wordpress.com. Each and everyone of them needs to earn their own credentials.

But when you use http://www.astrorobin.com/blog/ as the address for the blog, the blog and the main domain are associated with each other as far as search engines are concerned.

So if you really need to make a difference between the main page and the blog, I’d advise to use subfolders.

What do you think of using a subdomain as a blog site?

example: http://www.blog.astrorobin.com

Best Regards, Robin.