Blog commenting can actually help in the SEO of your blog or website. Not only have a lot of comments on your blog improves your rank in SERP but leaving a comment on other blogs/websites, especially on a related niche will also be highly beneficial.
How comments on your posts help your website
You have written 1000 word article, your article drives a lot of comment, let say you get 50 comments. Let say, each comment is 20 words, now the word count of the entire comment is 1000 words. The total word count on your page is 2000 words. Since google likes long content, your article is likely to be ranked higher.
How commenting on other blog helps
When you leave comments on other blogs, you also have an option to share your link. When you leave a comment on 50 blogs, you share your website link on 50 blogs. Now 50 websites are pointing towards your blog. You get traffic as well as improve website rank.
How comments on your posts help your website
You have written 1000 word article, your article drives a lot of comment, let say you get 50 comments. Let say, each comment is 20 words, now the word count of the entire comment is 1000 words. The total word count on your page is 2000 words. Since google likes long content, your article is likely to be ranked higher.
How commenting on other blog helps
When you leave comments on other blogs, you also have an option to share your link. When you leave a comment on 50 blogs, you share your website link on 50 blogs. Now 50 websites are pointing towards your blog. You get traffic as well as improve website rank.