Definition of DoFollow blogs and no follow

What exactly is the definition of DoFollow and NoFollow ?? Why, the bloggers seeking DoFollow blogs to target those blogs SEO Optimization ?? DoFollow understanding is that link that we enter when you comment that will be regarded as a backlink by search engines such as 
google or can be defined instruct search engines to give the effect of increasing the link target's ranking in the text of a hyperlink on its search engine index. 
While the definition of NoFollow is an attribute of HTML code that is used to instruct search engines to not give the effect of increasing the link target's ranking in the text of a hyperlink on its search engine index. And in general are setting nofollow blog comments, aims to reduce spam. Even though so, you still can change the nofollow to dofollow so anyone who commented will receive a small gift in the form of backlink immortal because it has been willing to stop by and comment. 
Now let's look at some of the advantages and disadvantages of DoFollow and NoFollow: 
Advantages And Disadvantages Dofollow Blog: 

1. Number of comments more particularly from opportunistic visitors who want to take advantage of free backlinks. This of course is in addition points to improve pagerank on our blog.
2. Most of the comments are SPAM and not quality
3. Visitors especially opportunistic visitors will be more frequent visits to leave a comment so that's growing
4. Google Page Rank will be lower due to the effect of page rank. But Google also do not like the blogs that have too many outbound links on a link to an internal appeal must be accompanied with a backlink from the outside.
5. Alexa rank generally fast down or low for this type of blog because the blog traffic means more crowded the better.

Advantages And Disadvantages Blog Nofollow:

1. The number of comments a little more and come from loyal blog visitors or new visitors who want to get acquainted or just blogwalking.
2. Better quality comments and general comments given for the contents of helpful writing or in the form of questions
3. Visitors are mainly loyal visitors or new visitors will only be returned if the blog content useful according to them
4. Google Page Rank will not be affected
5. Alexa rank generally slower down unless the contents of the blog interesting and useful so crowded with visitors.

By looking at the advantages and disadvantages of each type of blog mentioned above, it is now entirely up to you to transform your blog into a DoFollow or NoFollow. May be useful..