If you use a sub domain as your primary domain can this do any harm to SEO? Or id the only negative the obvious complication in the name? Thanks .
The complication in the name is a bigger problem. I think you will be fine with a sub domain. Just make sure all backlinks point to the sub domain
A subdomain is treated as a different domain by the search engines rather than as a directory or section of the main site. As zexy said, if you're going to use a subdomain to "wall off" part of an existing site, do a 301 redirect on the links to make sure they point to the new location and you'll most likely be fine.
subdomains are completely new domain because of this using a subdomain will not effect the main domain
They're not new domains. They're SUB domains. They're simply treated as separate domains by the search engines.
mm ok thanks, so I will be safe using subdomains over domains. This is because I want to make a large amount of automatic blogs and do not want to buy domains for each of them.
Yeah, that's fine. The first time I ran into the "separate domain for search engine purposes" was when I used a subdomain for a forum on a site I run. I noticed that the search engines weren't crawling the subdomain with my other pages, but were treating it as a separate site. Then last month, when I started building my own search engine site, I noticed that the spider wasn't crawling subdomains unless I explicitly told it to.
As dan said, the search engines treat a subdomain as an entirely different entity than your regular domain. Just be careful cross-linking too much, you can run into problems. I would suggest only linking 1 to the other, and not reciprocating too much if at all.