In SEO blog commenting is a part of off page process.Posting your comment on other person post and share your ideas within the community a good thing.
But if we take this as a strategy
“How Blog commenting really helpful to get backlink to your site” .Is this even possible or not.and how much a person has to spend time on that.
Most blogs and forums have all links in comments marked as nofollow, meaning that you will get absolutely zero SEO benefit from them. Of those that don’t mark them as nofollow, the chances are that the pages you are commenting have very low levels of googlejuice running through them, and that’s probably being shared out between loads and loads of links, so you will get as near to zero SEO benefit as makes no odds.
Any benefit is similar to your own blog - hinges on relevant quality content.
If your comments on other blogs are good, you may get some traffic.
If your blog content is good, you may get some that will link to it (most likely follow links).
Much easier on forums than blogs. Just find questions that people ask on forums where you can provide a good answer. Finding 20 such opportunities in a week is easy. With good answers a percentage of those reading your forum posts will click on the signature links to find out more.
Except that the OP is asking about building backlinks, not about increasing traffic.
Most forums are useless for backlinks because - like SitePoint - external links are marked “nofollow”. Even where they’re not, you’ll get very little benefit from any kind of link which you can easily place yourself. (See Stevie D’s post #2 about blog commenting - same applies to forums.)
To get really worthwhile backlinks, I’m afraid there’s no real substitute for creating a site with excellent content which other sites will choose to link to.
What purpose would there be in buildig backlinks other than as part of a strategy to increase traffic. Surely increasing traffic is the intermediate goal for any preliminary goal of increasing backlinks?
Anyway a nofollow backlink is still a backlink even if it is ignored by search engines - after all it is real people you want to get to your site. Getting the highest possible number of visits from search engines would serve absolutely no purpose whatever if you got zero real people visiting.
Too many people get so involved with the preliminary goal that they forget what the end goal is - people visiting your site and actually doing whatever you want them to do there (eg. buying your product). Preliminary and intermediate goals only work when they support the end goal. This is one reason so many people consider their SEO efforts to be a failure - because the end goal has been overlooked.
there is both direct traffic and indirect traffic by means of SEO. Of course the latter equation will continue to change, but as long as you’re able to have a link that people can see and click on, you will get some spillover traffic if your comments show insight and value