Backlinks from high PR but not relevant to your topic

There may be value in terms of the sheer number of inbound links, but only after you have thousands. Other than that, there is little, if any, value

Relevancy is very important now days if your link is not from relevant page then it is useless..

It wouldn't necessarily hurt your site but it wouldn't help as much as well. If you have high PR sites to post, then by all means post away. But if you have high PR sites with relevant content then it is much better. Relevancy not only helps with the rankings but it is also extra traffic.

Imagine a site with thousands of members there and your backlink happens to be sitting right there alongside a very thoughtful and quality content. People will click on that and that's added traffic to you.