I'm bit confused when doing link building process, because if some SEO peoples sit back in link building process, sometimes they say that relevant backlinks is very important in SEO. But I'm always do link building without that, I just embed my link and anchor text according targeted keywords in DoFollow page and have a pagerank, and it's not bad when I see the result in SERP. I think many peoples here have a great skills in SEO, and I think you have own opinions about relevant backlinks in search engine ranking factors.
It is very important to get links from relevant sites. Getting general or off topic links is not good for any site. It is not a good SEO practice.
Relevant backlinks affect your page ranking for your target keywords so they're important. It's not enough now that you can links pointing to your pages, you rank better if those links are relevant to your search terms and to your page. Hope that helps. Have a good day!