There are some reasons why we have to comment blogs and what we get when commenting someone's: We are all interested in optimization our blog, so one of the reasons - comments affect the SEO. You can show yourself by adding a link in your comment. That is how it works. People click you link and visit your blog, so they bring you traffic. Hopefully your blog will be interesting for them. If you don't leave a link on your blog just write a specific comment that will show your interest and be exact with topic. Commenting someone's blog which is related to your's by category attracts people to visit your blog, or at least start the conversation. The main point is that you can advertise yourself for free. Next time you look through comments and you will see what other think about your opinion.
Here is a relevant link under you post that will add more value to this post and also helps the readers of this thread to know more: www(.)aliciacowan(.)com/social-media-and-digital-marketing/blogging-and-content/blogging-comments
Yes, you can advertise/promote your site for free through blog commenting but that is not the primary goal of blog commenting. It's a great way to build links to your site, but beyond that is a more important reason to comment on blogs related to your niche: it's a way to build relationships. Blog commenting allows you to engage with your target market. You share your opinion and provide value to the discussion. This is how they get to know you more, and if they find your comments worth following, then they will click on your site to get more info. Hope that helps. Have a good day!
The only time I do blog commenting now is if the site and content is directly related to my site and I can easily add content in the comments that will interest people and potentially leave a link at the same time. Google might not be smart enough to pick up on everything now, but it is only getting better at detecting spam.