According to you what are the importance of sub-domain in SEO. Does sub-domain effects the ranking of website.

Sub-Domain is the best way to get higher ranking of keywords on Google. Google consider sub-domain first in search. Google penalize exact keyword match domain but through sub-domain SEO have option to target keywords. Sub-Domain is very important and quick method to push ranking high on Google.

 Benefits of Subdomains:

1) Total Web Domination - By having multiple websites, you have more opportunity to show up multiple times in a search engine results page, therefore pushing other websites down the page and achieving "Total Web Domination"
2) Local Optimization of each page
3) Google gives websites better PageRank if there are external websites linking to pages of your website, or links within your website, to other pages of your website.  In the case of multiple subdomain websites you would cross-link the sites to help each site get better Ranking in Google
4) The people running the local business can have control over thier own content.

1) Total Web Domination - By having multiple websites, you have more opportunity to show up multiple times in a search engine results page, therefore pushing other websites down the page and achieving "Total Web Domination"
2) Local Optimization of each page

If you have the good backlinks for your sub domains, you get more value for the main domain.