What role do "nofollow" and "dofollow" links in blog comments play in SEO?

"Nofollow" links essentially get ignored by search engine crawlers. They don't pass any link equity or authority from the linking page to the destination. Most blog comment sections automatically add nofollow to included links to prevent comment spam from manipulating rankings.

On the flip side, "dofollow" links do pass link equity when crawled. They signal to search engines that the source is vouching for and endorsing the quality of the linked page.

From an SEO perspective, dofollow links in comments can provide some minor ranking benefits if the linking domain has authority itself. However, most SEOs advise against actively pursuing blog comment links specifically for SEO value due to their generally low quality and Google's stance against awful link building solely for search rankings.

That said, including a link to your site or content in a relevant, value-adding blog comment on an authoritative site can still be worthwhile. It drives some referral traffic and creates a positively associated backlink, even if it's nofollow.

The bigger risk is overdoing comment link building and being seen as a spammer, which can actually hurt your SEO if you get flagged negatively by spam detection algorithms.

So in short- nofollow comments provide no direct SEO benefit, but dofollow links can pass minor equity if they are high quality. However, the overall emphasis should be on leaving authentic comments that add value rather than self-promoting through blog comments purely for SEO purposes.