do follow links pass trust, authority, and page rank. No Follow does not pass any value. More info here >>>>> youtube.com/watch?v=g37bwBlifnk
Dofollow and nofollow are the link attributes attached to a link on any website to assist the search engine about its quality. Webmasters use this service heavily to tell search engines whether the link posted on their website is a reliable one or not. It helps the search engine to determine if the website wishes to link their page to the mentioned link, so that the visitors could have more information about their desired topic.
Google and some other search engines pass little to no weight from nofollow links - even if you had a million nofollow links, it's possible your site wouldn't budge in google, while if those links were dofollow it would definitely help you.
Dofollow link allow PR Juice to flow back to your website and google will use it to determine the importance of your website. This will increase your website PR over time as well.
Any way, Dofollow is good for website ranking in search engines and, Nofollow links are bad for site ranking in search engines. For reason, read above comments.
I just recently converted my blog to a dofollow blog. Although I don't have a lot of traffic at the moment, I personally do feel it's very important. I think it benefits both the host and the person leaving the comment.